Pros - Deep sub bass, V sound signature. crisp highs. Carbon driver doesn't distort under pressure.
Cons - Most knock offs, Have to buy from Japan to get real ones.
I really loves these JVC HA-FX3X iem. I have been searching for something that can hit as hard in the sub bass as my desk 4.1 system, which I did find the Sony MDR XB950 over ear and the MDR XB90EX iem, but neither had the highs for the snare and high hat. I found the JVC HA-FX201 that has a great sound signature, but it begins to distort under huge sub bass pressure. (I make bass music)
I needed these because as the world becomes more cramped, it becomes less polite to blast sub bass into the neighborhood. Now I finally have a way of blasting my music that won't bug the neighbors and accurately recreates the sound I so love, without compromise. I ordered the newer HA-FX33X that will be here soon. I hope to review those as well.
Pros - Good bass and Rumbling sub-bass,fairly wide sound stage , clear separation. warm tone, Loads of volume. -no amp, Decent trebles, Build Quality
Cons - Small hissing b/g noise, a bit large for few people, muddy bass if pushed, trebles can be shrill at times - Its a JVC
After having sony mdr ex50's I decided I needed headphones with a little more punch for my electronic music. After listening to it once, I feel like there is nothing better in this price bracket with this much bass to offer. You can feel your chest tremble sometimes(it actually doesnt shake it), and it can sometimes be overwhelming for some. Overall, great headphones. Only downsides are the microphonics which are satisfactory due to the large air inlet leaking a little sound from outside, but thats here for the massive bass. When listening you cannot hear the outside noises much at all. I highly recommend these headphones if you are looking for a 50$ headphone that can compete with Beats and sound better.
(Edit, after listening to these for many months now, I have to say that the headphones have become much warmer in tone. Sound seperation also improves as I can hear more details and fine noises while playing music that I could not hear before. You MUST burn these in for at least 40 hours before judging them, otherwise you will end up with a distorted impression. Secondly, the headphone has the bass, it reaches quite low and can rumble your eardrums. I think it would have been better if they improved the quality of the bass as it is somewhat muddy unless you eq it or in my case xhifi it on android. But that is different. Stock, the iems can sound quite muddy like others state, but by following my tutorial on improving the sound (http://www.head-fi.org/t/671936/how-i-turned-a-bass-iem-into-a-balanced-clearer-iem), you can make these sound a whole lot better.