First of all, I love these headphones. I'm using it on a daily basis. Mostly for bass heavy electronic music, like noisia, phace, fourward and similar. I also like movie scores like alien resurrection, revenant, most of the junkie xl scores (mad max:fury road!) these are also bass heavy and orchestra pieces. Sometimes I listen classical and jazz, which is still great, but all of these needs eq for me.

My best source is my HTC m8 with PowerAmp. I also have a babyface pro interface, but this phone with the eq algorithms in PowerAmp is unbeatable.

For classical and jazz I prefer my Beyerdynamic DT 990 pro with the babyface pro, but that is not a mobile headphone.

So this is not neutral. By default, it has a little more bass, little more high mids and less highs. Without eq I wouldn't like so much. I put extra bass on it, and it can handle that well. The bass is in your brain. I remove some mids and add some highs.

Since it is closed, I can use during work next to my collegaues. They can't hear anything. So the isolation is really good.

After some time, it is a little constrict and need to be take off for few minutes.

So everything with this IEM is just perfect except the low highs. For me, it is so harsh, like a very cheap IEM. I'm very sensitive about this.
I listen classical, jazz, chill out, breakbeat, progressive house. It is pretty hard to find IEMs which satisfying my needs.
I need exceptional bass quality, warm sound signature, great soundstage. Unfortunately this is not like this. Even the t10i has this problem with the highs, but a little better.
 
After few hours of listening, it became a little better, but I decided to send it back. (I also tried later in a shop with a more used one, but it is the same annoying low highs)
Instead, I bought a Yamaha eph-100, which doesn't as good as the RHA MA750i in the other things, but the sound signature is perfect, and it seems that is the most important for me.
 
I used an old Sony MH750's tip. All the other tips are useless for me which came with the RHA. 
 
I hope RHA can fix this problem later, because I really liked everything else.