S0 is the new little brother of S5 which I quite enjoy. It costs about half the price of its big brother, at US49.50. It's great to see more competition in the sub-$50 price range, because that's how much most mainstream consumers are willing to pay for a pair of good earphones/in-ear monitors.
 
S0 has the same flat cable as S5, which may take some time getting used to compared to the traditional round cables. There's some microphonics even when worn over the ears, but adjusting the cinch upwards makes it a lot more bearable just like S5.
 
While the housing has left and right channels clearly indicated unlike S5's tiny letters that were very hard to see, S0 doesn't have any tactile way of knowing which side is which. I prefer to have that because it may not be possible to see things in the dark. I think isolation is very good. It came with different standard silicone tips, including a set of very nice Comply S-400 foam tips. I quite like the default tips (with the red colour), normally I would rather pick Comply tips. Like most IEMs,it’s very easy to drive.
 
It has the sort of balanced sound found in S5. This is a great IEM for portability and easy listening.
 
Bass is definitely not deep like S5, but it's there. It's warm but not bassy. Good control. Like most balanced phones, it excels at classical music, instrumental, etc. Low-mids are a bit grainy, vocals are excellent. Treble is just as smooth as S5. Even with the silicone tips I'm using, it doesn't sound harsh or sibilant unless the recording is that way. Like S5, imaging is very good. 
 
There isn't much else to talk about with S0 because it does a good job with most things. 
 
For $50, you get a pair of jack-of-all-trades IEMs. Due to its balanced sound (even more so than S5), it is suitable for any genre you throw at it, except for bassheads. If you just want more bass, this is not for you. I do believe most people won't find this IEM offensive. It's very likeable, reminds me of Soudmagic PL-30 I owned a long time ago, with more warmth and intimacy (more bass & treble). Because there are so many choices in this price range, you'll need to buy according to your favourite sound signature. If you're a newbie who can't decide, then this may be an option as your first journey into audiophilia.

Design and Comfort
S5 is a new higher-end in-ear-monitor from Brainwavz retailing at about US$100.  I’m glad Brainwavz has offerings at most price points below $200. It's great that companies such Brainwavz and SoundMagic help bring down prices; if not for them, we would still be paying an arm and a leg for these things.
 
It has a flat cable instead of the normal round cable, similar to the new Creative Aurvana Live! 2. I don’t know if this is a trend. I’m more used to round cables, but round cables do tangle a bit, except really thick ones like the ones used on HM5, so I think flat cables do have an advantage here if you want your cable to tangle less.  Microphonics is minimal, slightly more than Brainwavz M4; however, that can easily be solved sliding up the cable cinch (e.g. during exercise).
 
The IEM’s housing has a flat side, which comes in handy - a tactile way of identifying left and right earpieces. All you have to do is have the flat side facing outward when worn. The letter “R” and “L” are extremely small, but you just need to look at them once and you’ll remember which side is which by looking for the flat surface on one side of the housing. Isolation is excellent, at least 25dB, basically similar to earplugs. If you’re looking for an IEM that isolates noise like an earplug, this is an good option for you.
 
It came with an assortment of different standard silicone tips, including a set of very nice Comply T-400 foam tips. I’m using the T-400 for this review, while I use S-400 on my M4. I’m a fan of Comply tips, and I prefer foam tips to silicone tips in terms of comfort and sound. Silicone tips do, however, bring out better highs on most IEMs (if not all), if that’s what you’re after.
 
It’s very easy to drive, coming from relatively easy to drive headphones. It’s louder than M4 at the same volume for example.
 
Sound Quality
Straight out of the box, I couldn't really fault it much. I’ve done over 150 hours of burn-in. DAC is FiiO E10. There are some similarity to Brainwavz M4, could be considered an upgrade in every way, except I prefer M4's mids.
 
Bass is deep and tight, probably a tad more than what you call neutral/flat, not unlike CAL!2. It's perfect for people who like to feel their low notes.  I don’t find the bass to be distracting; in fact, I can really appreciate the detail in the bass. Unlike M4, you won’t find a mid-bass hump in S5.
 
Midrange is slightly warmish, without any bloated mid-bass. If I had to complain, this would probably be the weakest link of S5. You're not going to get perfect sound at any price, let alone at this price range.
S5 is less airy than M4. That’s expected of something that blocks 90% of all ambient noise. For me, I do prefer my mids to be more airy, so I’m biased. I guess that’s the trade-off between isolation and soundstage. 
 
Treble is very smooth with the foam tips. No sibilance at all, but detailed enough to show it if the recording has it. With silicone tips, the sparkles are brought out, more so with the the tri-flanges.
 
While soundstage is quite intimate, I feel like I’m listening to music in a studio environment.  Due to its excellent imaging, some recordings sound a bit binaural. I thought was sitting next to the pianist, facing the other way (away from the piano). Classical and country sound so good, especially piano pieces.
 
Conclusion
This is a very likeable IEM for mainstrem music-lovers, regardless of your preferred sound signature, in my opinion.  Is it for bassheads? Sure, if you like quality bass with enough quantity but not overly so.  Is this for treble-heads? I reckon B2 is a better choice. The sub-$100 bracket is such a competitive price range, these days you can get headphones or earphones that would have cost you several times more in the past. If you were to buy just one IEM for portable use, this would be my personal choice for portability. It's good at most things, and excels at sub-bass.

Sound Quality
Straight out of the box, it sounded great, pretty much like the original CAL!. I’ve done over 100 hours of burn-in. DAC is FiiO E10. As I mentioned in one of the posts, it reminded me a lot of Sennheiser HD 25-1-II. This can be a headphone for people who really appreciate bass (bassheads included).
 
Is this a neutral can? No, but it is definitely a fun can with a V-shaped signature. Most people on Head-fi claim to prefer neutrality, but the truth is a V-shaped response is perceived to be more balanced due to the equal-loudness contour.
 
The bass is deeper than even the HM5; has better extension than the original CAL!. I could feel the tactile low notes more at 20-30hz with the CAL!2.  The bass is excellent, tight and punchy. It’s got both quantity and quality, which is highly valued in the audiophile world. HM5’s bass is cleaner and tighter, whilst CAL!2 decays better.
 
I can’t really find much fault in midrange. The vocals don’t get drowned out by the bass or treble. There’s no detectable boom or muddiness in mid-bass. The warm signature makes listening to genres such as classical a bliss. I was rather surprised.  With bass-heavy music, it sounds just like you’re in a club (or places with good PA systems).
 
The treble is sparkly like the original, a tad more so than the HM5. Voices are airy as should be, while the high notes are by no means harsh or fatiguing; your mileage may vary. The bass, on the other hand, can get tiring after long listening sessions at high volume, for those unbalanced bass-heavy songs (which describe most contemporary music nowadays unfortunately).
 
The sound of CAL!2 is a lot fuller than the HM5. CAL!2 is more intimate; whereas the HM5 is more distant sounding and overall thinner. Though it doesn’t sound as open as the HM5, some people criticised the HM5 for its artificial hollowness. I guess I might be too spoiled by HM5.
 
CAL!2 is also great for gaming or movies. For competitive gaming, you would probably want an open bass-light headphone instead. For casual gaming or for pure immersion experience, this has the fun factor to bring it all out. The same goes for movies. Dialogue isn’t a problem. Cinematic effects are fantastic.
 
Conclusion
The sound is lush and sparkly. I think if you loved the first CAL!, you’ll love the new version. CAL!2 took what CAL!’s good at and improved upon it. Although I recommend buying the original CAL! if your budget is very tight (<$100), this upgrade is worth the extra money (with diminishing returns like everything else in the audiophile world). It has plenty amount of quality bass for the mainstream listeners while maintaining a clean and clear sound throughout the audio spectrum.
 
There are also premium models available that have active noise cancelling and wireless features – Creative Aurvana Live! Gold and Creative Aurvana Live! Platinum. Gold has the same driver as CAL!2 but Platinum has a 50mm driver, which potentially could mean better sound, similar to D2000/D5000/D7000? In my opinion, if they put the 50mm in the CAL!2 and let the Gold and Platinum have extra non-audiophile features like wireless and ANC, that would be perfect for us.

Miscellaneous:  
They came in a tube-like container. There are only three pairs of silicone tips, although they are quite comfortable. The material used is softer than that of PL-30’s. The housings are open at the back so if you use them on the go, there would be wind noise coming through.  As I have grown accustomed to over-the-ear designs, an ear glider would have been nice, but at such low price the accessories are reasonable.  The only difference between MEElectronics M2P’s and M2’s is the P version has a built-in microphone, useful for when you use them with a mobile phone. Almost forgot to mention about the cord, it's sturdy, it's braided, and more importantly, it's not rubbery, that simply doesn't intertwine or is hard to untangle.
 
Sound:
M2P’s sound settled during the first 10 hours of burn-in, as a result the bloated low end and instrumental congestion have pretty much disappeared. However, the bass can be uncontrolled at times. The highs are not as smooth as I wanted, yet the overall sound is better than most of the stock phones. Soundstage is more like headstage where music is played inside your head. That would be a plus when you desire intimacy. Essentially, all the basic elements are present.
 
Verdict:
These might be the best lowest budget earphones that can be called "real" earphones, giving out acceptable amount of detail for those who are still using cheapos. I suggest people get M2P’s or M2’s as back up pairs since they only cost minimal with a discount or coupon. If you are just starting off with in-ear phones and don’t want to break the bank, you ought to take these into consideration. They are also an excellent replacement for the iphone ones. The cord alone is worth the price!

Miscellaneous:
They are exceptionally comfortable and light; when I wear them I sometimes forget they are in my ears. The quantity of accessories is more than enough, though the quality of which is not so. The tips seemed poorly made, and one of the bi-flanges even has some defect. I only found the olive-like foam tips to sit snuggly in the ear canals. Isolation is above average with those tips, but the sound would be darkened because of that. The cords tangle quit easily such that I had to separate them almost every time, but this problem improved after more than a while.
 
Sound:
The soundstage is wide and airy, which is probably is the most noticeable aspect and one of the main selling points of PL-30’s. Bass is tight and controlled, yet light as well. With a lot of burn-in (100 hr mark), bass is even tighter, and better quantity-wise, still incomparable to many.  Another feature of the PL-30’s is the adjustable bass knob. When pointed inwards to the strain relief that’s called deep bass, whereas clean bass when pointed outwards. Most people would prefer the clean bass, as everything is less-veiled. On the other hand, deep bass made little changes to the bass impact. The higher range is never harsh. I find the mids and highs well defined and likeable.  The depth makes you feel near the stage rather than someone singing in your head. Like many budget IEMs, ultra-high treble is rolled off, which means anything above 12000Hz is inaudible. That's not really something of significance to the average consumer as the highest fudamental note that an instrument, namely piccolo/piano, can play is just about 4000Hz, anything above 6000-8000Hz is just harmonics.
 
Verdict:
PL-30’s were first introduced as Shure E4C equivalents, which is something many would disagree upon.  I personally think the PL-30 could have been over-rated to some extent because the popularity died out after the initial spike.  They were nevertheless one of the better valued IEMs around early 2009, since then there has been a lot of competition rendering PL-30 not as highly competitive before.  This is not to say PL-30’s are no good, on the contrary, for about $25 they offer balance, detail and a massive (for the price) soundstage.

Miscellaneous:
Brainwavz M2 is the repackaged version of ViSang R03 with identical IEM component. These are quite comfortable, but they are not light per se. I also decided to (carefully) cut off one-fifth of the length of the long strain-reliefs. The accessories include three sizes of hybrid tips and three sizes or foam tips (they are similar to olive tips). I am happy with the medium size for both; however, the small foam tips are so small that I can’t think of any adult would find them fit. It would have been better with a spare pair of either the medium or big. I never found plastic tips to be comfortable compared to foam ones, but this time I actually prefer the hybrid tips than the foams. Unlike the cords of PL-30 which tangle quit easily such that I had to separate them almost every time, the cords of the M2 has memory of its own which retains the shape for a long time. I didn’t think it would annoy me this time. Although they are strong and similar to those of full-size headphones, I much prefer the cords of the Meelectronics products.  The plug looks better than the usual 45-degree ones, and don’t stick out as much. The overall build is sturdy as heck. Isolation is along the lines of PL-30, but with wind noise susceptibility due to the holes on the phones.
 
Sound:
Before burn-in, these are really relaxed and the bass was quit strange. After enough burn-in, they opened up somehow and the sound signature stabilised. I have done more than 80 hours of burn-in now, I am very satisfied with their strong suits – bass and midrange. The bass is sufficient in quantity, and the decay is perfect for Hip Hop and R&B music. The bass is there when needed, and since the signature of this IEM is towards warmth, a veil is inevitable, which is not a problem at all for me. A friend of mine tried them out, and thought they are not as good for classical as the ones he’s got (not sure what IEMs, but I assume brighter than M2).  The vocals are very sexy and enjoyable. On the other hand, treble may be tamed and may lack a sense of sparkle, yet it is decent nonetheless to my liking. I personally hate fatiguing phones, so I’m a bit biased. The roll-off of treble is later than I expected at around 14-15 kHz, so the M2 is extended both ways with deep bass and high frequency harmonics.
Apart from the veil that I talked about, there is however room for improvement on the soundstage. Although the soundstage is better than average, I still crave for some full-size cans’ or speakers’ experience in IEMs which I will probably never get. I will address these in my next upgrade. The distance is about first couple rows, yet not as distant as the PL-30.
 
Verdict:
Most people would agree that M2 is one of the best sub-$100 IEMs you can get. For the price I paid, I am more than satisfied with these bad boys. I only got it on Tuesday last week due to the problems with the Australian postal service where they got sent back to mp4nation without any reasons from AusPost, and I’m glad to receive them eventually. Mp4nation is good enough not to ask me to pay extra for the postage for the second shipping.  For the low price tag, and given the right sound signature for you, M2 is what I recommend to someone who is very conscious of value like me.