Pros: Sound quality, build quality and fit.
Cons: Expensive but it's good to the point they actually feel value for the money
I have owned the UM Miracle for about 2 months now, I have bought them from Stereo Singapore and I have to say the service overall is great and altogether it took roughly 4 weeks to arrive after sending in my impressions. It is good dealing with Stereo as hassles such as having to mail your own impressions and handling the shipping is negated and the price they charged is also much cheaper than the online price of US$1049 and on top of that I got a 10% discount which was sweet. For the the customisations I have went with the classic transparent with midnight blue/wine red tips.
Source wise I use them with my Sony Walkman A16 and iPod Touch 5th generation without use of an external amp/dac as I've always felt those added to the bulk which affected portability a lot. As for the sound, using mainly the Walkman A16 the soundstage as mentioned from other members is very wide and when you close your eyes it actually feels like you're in a concert hall, with the music touching you as if it was real life. I've to say this experience isn't something you get from many CIEMs or IEMs out there.
As for my previous CIEMs/IEMs I was using the ATH-CK100pro, AAW M20 and Westone 4R(for a while before selling them) and they are just not the same again after receiving my Miracles. The Miracles have somewhat obliterated the other 2 from my ears and the use I get for them are almost non existent now, that just really proves how good the Miracles really are.
As for highs they are rather smooth and extended without being piercing at all, it is actually one of the strongest points of the Miracles as compared to the other frequencies. Pianos, violins, and other string instruments have never sounded that good before.
While many users have stated that the Miracles have a slight V-shaped signature and some have stated that the mids are somewhat 'boring'? I personally do not feel this way as the mids on the Miracle are actually very neutral and accurate, it lacks the "oomph" of certain mid-centric IEMs such as the fitear TG/MH334 or Westone 4, I feel that with those IEMs mids can be overly warm at times and sometimes even muddying the sound. For the Miracles they're very clear and gives the Miracle a sense of positive overall clarity in conjunction with it's somewhat sparkly highs.
The lows as many have stated are not for bassheads and since I'm far from one(I actually prefer less bass usually), I feel the bass on the Miracles are definitely far from nonexistent but they do exists in a just right amount while being tight and punchy at the same time, this gives the overall vibe that the Miracle is very balanced and neutral as compared to many other CIEMs/IEMs. They still do extend very deeply and mid-bass never gets in the way with the other frequencies.
So as stated, the Miracle is a very balanced CIEM with no frequencies disrupting the other in any way, each frequency is able to sing at it's full potential which really makes it a wow factor for the Miracle.
I can say that I have came a long way before actually settling for the Miracle and I have tried many other CIEM demoes out there and the comparable ones in price would be the JH13FP, UERM, Noble 4, AAW W500 etc. and personally I can say that I prefer the Miracle to the above stated CIEMs(demoes) as the Miracle just appears so balanced, yet being able to produce a very engaging 3D soundstage that it really gives the others a run for their money. It therefore doesn't surprise me that the Miracle is able to stay at the top for such a long time and even newer and pricier alternatives from UM themselves have really failed to impress as CIEMs such as the mentor and legacy did not lure me away from the Miracles.