You can't ask more of an IEM. Agreeable that its Ultra Premium but gives you every bit of return. Excels in all respects Comfort, Build, Sound. Haven't tried it with a DAC yet so the best is yet to come. Delivery was super fast - less than 24 hrs.

In the age of multi-driver technology IEM's, a single dynamic driver IEM & that too of a price it is at, is not only an anomly but will also be viewed with suspicion.
I too had my own doubt, but my search for a capable IEM was ongoing & wanted to purchase IEM that were sold with warranty (Products unavailable in India that cost lakhs, imported & that too without
warranty is too much of a risk to bear).
Product that I purchase without trail, like this, if for any reason I personally cannot find satisfaction then I sell it off. Solaris OG, Solaris 2020, Fiio FH 7, Fearless S8F, IE 800s, Mest MK II etc are some of the IEM's I previously owned & sold off either due to wearing discomfort or for how it sounded.
IE 900 after first few listens came across as lacking in impact, scale & cohesiveness. With Balanced Armateur(BA) sets, burn-in has not made much difference, but with IE 900's dynamic driver few days of burn-in truly changed the whole dynamics of sound produced by this IEM. I can assure that it was not me getting used to its sound, as I mentioned earlier with any audio product especially IEM or headphone if I don't find the sound produced endearing, then I just sell it off.
After burn-in the true character of IE 900 was revealed as having reasonably wide soundstage, extremely clean sound reproduction and a high level of musicality.
All this ends up being an IEM that is truly capable of delivering the true essence of any piece/genre of music.
Treble is well extended but never came across as harsh or sibiliant, never. Mids are extremely detailed & vocals sound extremely real. Bass has superb amount of energy & if a track has bass, be rest assured it will never shy away
from reproducing it with an impact. This IEM being extremely light & small, it has to be hands down one of the most comfortable IEM's you will ever come across. Even in sleeping position, this IEM never causes any problem.
Last but not the least, this IEM like may others depend on good eartips for it to sound great. Any eartip that dosen't seal well or dosen't allow IEM to rest properly can make it sound wonky & wrong.
Provided eartips do not do justice to this product. Many have rasied this point & I concur that provided silicone eartip is underwhelming. Foam eartips are better, but for excellent results I defentiley recommend Comply 500 series round eartips. I suggest buying large ones because irrespective of ear size, it fits easily & seals well. Usage for even long hours is convenient.
All in all, this is definetly a keeper, plus the provided balanced cabels & 2 years of warranty definetly deservers an appreciation.

This is a review of both the IE 300 and the IE 900. I'll copy paste it in both sections.

Firstly, accessories (ear tips and cables) are a massive middle finger from Sennheiser to the buyer. The included silicon tips are absolute bottom barrel trash. They can not seal for me and while pulling one off the IEM it ripped the tip from the stem. The foam tips are useful and help me get a good seal, but I'm using them sparingly, because, like all foam tips they won't be too long lived. Replacement tips?

The cable is sticky, tangly, fights you at all times. The cables of the 900 feel a little softer and less sticky, and there are 3 of them, but still these are far form decent for the price. Sourcing a good replacement cable will be a problem because of the non standard termination. I have bought a replacement cable "Tiandirenhe cable for IE 300, 600 and 900". It feels flimsy and cheap, and I'm not hopeful as to it's longevity, but that cable in feel is a humongous upgrade. I fail to see how a leader in the audio industry is so clueless. I was reading a discussion on a forum where Sennheiser reps., on being asked if they could recommend a replacement cable asked a person what the problem with the stock cable was.

Both the IE 300 and IE 900 are comfortable and after trying different ear tips I've found the best ones for me are the included foamies and Spinfit CP100 plus. It's unfortunate Hpz doesn't sell the CP100 plus. Also sourcing the original foam tips might be a problem. The seal is fidgety and while I can maybe attribute that to my ear shape being wrong, these aren't my first IEMs.

Sound is simple. both of these are basically detailed, pleasant with a good amount of bass. Having said that The IE 900 is FAR better than the IE 300s. More resolution, better imaging/ staging and bass. So much so that IMHO the IE 300 are bad value at their price and the IE 900s, while not good value get a pass because the summit fi section has insane pricing anyways.
In fact I thought my IE 900s were broken and were imaging off centre because of the extreme positioning capability. I sent them in for warranty and they returned them saying its fine. I was still not convinced and as a final resource played tracks on mono. the image was dead centre. Basically when you have multiple vocalists close to centre, the IE 900 can locate them precisely.

This review sounds ranty, and that's unfortunate. The headphones are good but are let down by the absolutely trash accessories. They could learn a thing or two from brands like Fiio. At least the carrying boxes are pretty.

Bottom line. IE 300s, OK, but 10k chi-fi is competitive. IE 900s, GOOD. They know it and have priced them accordingly.

These are some of the best IEMs you can buy, in a class of their own. sound superb and unique. No fatigue while listening. They also look awesome.