I can see people feeling that the EX1k is really uncomfortable. A lot of times the tip selection and insert depth matters. But also the natural earcanal shape. I guess I'm sort of lucky both of my ears are pretty straight? Also, on top of this I usually go with small tips and a very deep fit. Going as deep as almost a CIEM-like insert depth. To me it kinda reduces the sibilance that many people felt and additionally to me it sounds really dynamic. Especially after the removal of the foam dampers inside the tube. All in all, I used that more than a few hours at a time on many occasions
Personally I really think it's one of the best IEMs out there when it comes to detail retrieval and perhaps EQ-ability
I'm still miffed that I sold mine a while back...