Most about these IEMs is already said in many reviews already out there so keeping it short. SQ is brilliant. Sounded clearly a notch better than Shure SE215 to me. Could easily be the best sub 100$ IEMs out there in terms of sheer sound quality. Lacks in isolation department. Knocking off the half star just because, at asking the price, the design could have been better from durability perspective.

It lives upto its name. This ne is a gem as far as neutrality is considered most neautral Amp i have had or tried so far. I have tried HiFi man EF5 Fiio E11, E17 ,little dot mk2 etc. and found them clearly sub par comparing the bar this product has raised for its price. The immediate this one can notice is great improvement in both treble and Bass. Bass is quite tight. Treble is cold and accurate. Might sound little harsh for headphones like ATH50 but suits well enough for HD650. Wanted to try out well known tube amps especially Schiit Valhalla, Bravo audio ocean and the HD650 specialist (as per many folks on forums) Bottlehead crack. Unfortunately they are not easy to find in the part of the world i live. and i am not much into DIY either.May be someday i'll get my hands on them and then compare the famous tube sound signature with this little beast's accuracy in terms of SQ and see what suits my ears more, accuracy or the warmish (yet close to accurate) sound. For now i'd safely say this is best in class Amp and a great value.
 
Let's look at its shortcomings.
1. the charging mechanism has not LED indicator to show whether charge is full or not or whether it's charging or not for that matter. It  gets really annoying that i have to keep it off while it's charging and yet i don't know whether it is actually charging. It in fact most of the times is charging unless the heavy adapter has lose connection(it is quite possible as the adapter weighs more than O2 itself.)  or you forget to switch the button on (like i have done couple of times )For a 130$ product this wasn't a big feature to ask. 
2. Gain switch is useless IMO as it totally screws SQ I never needed it though, HD650 can get enough juice on 2.5X gain setting. 

I have so far had owned only FIIO products E10,E11,E17 etc. have tested out audioengine D1, matrix iDAC and some other DACs before purchasing this DAC. This is hands down best performer of all the products i have owned or tested so far. When you plug it in you'll definitely notice significant improvement in quality. Even by comparison of the other DACs and the way they improve overall SQ. None of them have given me this noticeable improvement over my  laptop's default Soundcard's output. It's not that E17 or Audioengine D1 didn't improve SQ, they in fact did (and not small by any means) but the jump is not quite as high as this little DAC. For the asking price i don't think one would ever find a product as good as this one. Bass sounds just so awesome like never before. It is tight and one can easily notice the improvement in the bass quality. Soundstage gets bigger and treble is accurate and when plugged in, my HD650 starts sounding a different headphone (the lush signature is still intact even if treble gets a bit more sparkle).  I am not much of into highs i like the way they are represented on HD650 without any Amp/Dac.But still treble sounds more accurate when plugged in with this DAC. Must say i am amazed with ODAC, 

Awesome headphones. Perform a lot better with good amplification. Good for almost every genre of music. Bass response is already good, can get even better and tighter with amp. Extremely lush sound signature. You can spend hours with it without getting fatigued by sound. Treble, though sparkling, sounds bit rolled off but that's how they can be so relaxing to keep listening forever. Only area where these headphone leaves you feeling want more is build quality. Plastic used is strong but at the price tag doesn't justify the use of plastic.I really liked to see what Sennheiser done with Momentum they could have done similar with looks department of these headphones after all its almost 10 year old design.

Truly premium feel of overall looks and packaging. Case is nice. It has got 2 sets of cables, one with the microphonics other without it. For the price the only complain i have is they are not as portable as Bose Quiet comfort. Other than that these headphones are great.
 
I actually went to buy Sennheiser HD-25 1-ii(Adidas Version) but ended up buying this one as the effective price difference was not much(Momentum was 'ON SALE' item).
 
Sound wise I won't go in much detail as there is enough info available already and I have same opinion for most part of it. They sounded on softer side compared to sennheiser Hd-25 1-ii and more laid back sound which is ideal for longer listening. Clarity was great as with many sennheiser headphones.They do not get as loud as Senn HD-25 1-ii though. Overall great for the price i bought them. 

As the title says, it's for Bassheads. Very fatiguing for longer listening. The amount of Bass on these just kills the fun for me so not very highly recommended. 

I was initially confused between HD 558 and HD 518 at the time of buying, but then some articles and forums on Head-fi helped me to decide for HD 518 as these were best bang for the buck and HD 558 did not justify their cost premium over these in terms of quality.

Design : Cord is detachable. Body is made up of plastic, so they are very light when you compare them with their looks. Plastic used for these is good quality plastic. Head band gives a little scare but It's not delicate, just not as strong as it should be. The grilled design is unique and looks good to me.

Comfort: Head Band cushion and ear pads are very soft and you won't feel sweaty or uncomfortable for listening sessions even more than 3-4 hours. So pretty much comfortable.

Audio Quality: 10/10 for the price. Sounds overall a tad bass heavy for audiophile standards but not much.

Value: 10/10 again without a doubt. Currently at 60 USD. so no brainer.

Slightly better than E10. Sound very similar to E10 just with more balanced sound. Tricky to get a good fit but for price and the quality they present, it is not that big deal.

First of all, I'd like to thank 'H20Fidelity' who recommended this IEM to me. I was not sure whether to go for this brand as i did not hear of it before. but thought of givin' them a try. Got it under 40USD. I had Sennheiser Precision 300-II before these and I liked them but i lost them so needed new pair with similar sound.

These are definitely better than my now lost Senn They are very engaging and ideal to listen music on the go. Bass is plenty (not by Bass head standards) and has a nice punch in it, which is more than sufficient for me. I'd highly recommend them to anybody who is on tighter budget.