So i bought the pistons 3 a week ago. The unboxing experience was stellar just like the older version, I was slightly disappointed that the chocolate smell was not present. Oh Well!!
 

 
Build Quality:
 
Build Quality is really good in my opinion. The braided cable feels durable and the strain reliefs seem adequete. I know that these are not made of metal, but I'm perfectly happy with the matte black plastic material. It has that understated look that i really like. You get three extra eartips at small, medium and large.
 

 
Comfort & Fit:
 
I think this is the most significant improvement from the previous version. It fits a lot better, like a loooot better. The P2 used to graze my ear at times, the P3 are perfect though. The cable does let out some audible wind noise quite a bit though. Isolation is decent, not as good as my RHA MA750i ( which is goes around your ear)
 

 
 
Sound Quality:
 
The sound quality is better in all aspects when compared to the Pistons 2. The Mids are no longer recessed which i really like. The Bass is tighter and punchier and the highs are not sibilant. This results in a really natural sounding and pleasing sound signature which sounds more fuller and neutralish when compares to the P2. The  Soundstage, seperation and details are also higher.
 
When compared to the pricier Sennheiser CX 3, the CX 3 is technically superior with more detail, soundstage and punchier bass, but i prefer the natural sound signature of the pistons 3 over the V shaped signature of the CX 3 the mids of which are quite recessed. The build quality also seems better than the CX 3, so i found myself listening to the pistons 3 more.
 
Conclusion:
 
Overall the new Xiaomi IEM's offer fantastic value which punches way above its price range in sound and build quality. Another Giant Killer, Well done Xiaomi!! 
 
 

BUILD QUALITY & FINISH
The new momentum IEMs are quite an interesting pair of earphones. The momentum series is known for its striking design and the attention to detail and this carries forward to the in-ears as well. The red and black metallic finish is a nice touch and turns heads. The build quality is quite solid ( it looks like metal bit its actually mostly plastic), the cables aren't removable like with the Shure se215s but the semi-flat design ensures they don't tangle as much.
 
FIT
They plug in directly to your ear. They have pretty large housings and stick out of your ear a lot, so i did find it easy to dislodge the iem's when its in your ear. It's definitely not as secure as some around ear cable design like how i wear my RHA ma750i, which is definitely a lot more secure. It isn't the best iem in terms of comfort
 
SOUND
 
Coming to the Sound Quality, the momentums have a V shaped Sound signature which means the bass and treble is more emphasized. This makes for a energetic and lively sound. The momentums can come off as slightly too treble forward or bright for some. I feel that the s notes are slightly irritating. Some heavy metal songs which use a lot of cymbals can be a touch sibilant and sound metallic.
 
The bass is, i think, the best part of these iem's. Its tight and has a lot of detail and texture. It does not feel overdone and gives a warm and punchy sound. I dont think it bleeds into the mids much. It makes the music very dynamic and engaging to listen to. It has a good amount of both mid-bass and sub-bass
 
The mids are also good. They have a lot of detail but might feel a little distant because of the emphasized bass and treble.
 
Noise isolation is pretty good with the right sized eartips
 
CONCLUSION
Overall i think these are an excellent pair of earphones at 99$. I do prefer the RHA ma750i as i think it has better build quality, better fit, better accessories and slightly better soundstage and slightly more natural sound, but its also more expensive.
 
Also this is my first review. Any suggestions and comments are welcome