Pros: Inexpensive, light weight, fairly comfy - no inner-ear fatigue, S-M-L expanding foam tips included.
Cons: A bit small which makes it difficult to put in the ear by pinching between tumb/index, some cable microphonics, cheap plastic construction.
Isolation on these is pretty decent, which I can't say I was expecting them to provide as much as they do. Compared to the Sennheiser PC-350 headphones that came with my Xonar Xense, they are 10x better at isolation!
Design... eh.... they're nothing snazzy, but you're listening to them, not wearing them as a fashion accessory They are fairly discrete so there is that, for anyone who doesn't want something shiny sticking from their ears.
Comfort isn't too bad either. Their light weight and shape make for long hours of listening, and you'll definitely forget they are in if you're just listening to music. The Sennheiser PC-350 are so uncomfortable after just a short while that it's hard to forget they are being worn. They might 'break in' and fit better, but as of right now they squeeze on my head too tightly and --as odd as this will probably sound-- cause JAW fatigue and not ear fatigue! My jaw bone on both sides around the joint just starts aching and I'm constantly having to shift them around, not to mention they don't seal with my glasses on so I have to wear them all goofy Needless to say, neither of those are a problem with IEMs like this.
Sound quality... Well this is where things certainly surprised the hell out of me, but not until now, nearly a year later... On vacation I only had a cheap, old, MP3 player and a computer that I would listen to music with. The MP3 player has nice sound, just it's AAA battery mean it lacks any oomph! The computer, well it's a RealTek chip and they aren't as impressive as VIA's EnvyHD codec IMO, so basically I wasn't able to get a solid impression of how these sounded. I had came across another old pair of earphones I got a number of years ago from Coke Rewards, V-Moda something-or-others whose name emphasized it had lots of bass, and they do... overwhelmingly so. Since I recently got a Xonar Xense (with LME49720HE OpAs) I decided to see how they sound, which I was reminded of why I didn't pay much attention to where I put them That got me thinking about these Marshmallows and so I dug around for them and plugged 'em in! Initially I was rather impressed that they both had some solid bass, something my SE210s lack, but also mids and highs, which the SE210s do very well. After adjusting the Foobar "Graphic EQ" a bit I came to a very solid configuration. To get those V-Modas to sound as if they had any sort of mids or highs, I really had to crank up those bands, in addition to still dropping the lows so it wasn't as washed out. These Marshmallows though didn't require too much really, and I managed to set it up so it sounds amazing in all the different types of music I listen to (not that they span too many genres, but bands like Crystal Method, NIN, Tool / Puscifer / APC, and Armin van Buuren's A State of Trance EPs). Honestly, I hate to admit it but I prefer these to my SE210s I have some E2Cs as well, but they had a run in with a puppy and were why I got the SE210s, but I later jury rigged the cables back on and soldered them up. Not pretty, but they work, and these sound still a bit better than the E2Cs as well!!
Conclusion: For $20 or less, you really can't go wrong. If you are looking for a <$50 pair for listening that you don't care if they get damaged/lost, but still want good sound, I think these should be on your short list. However, I will add that I only was able to realize their potential once I got them plugged into a source that had the ability to drive them. A high-end PMP, good phone or a portable amp will no doubt provide these what they need to sound as good as I'm hearing, but don't expect too much from a tablet or a typical computer audio codec.
I'm now questioning whether or not I should bother with upgrading from my Shures....