I have these headphones for a few weeks. I have been using them on a daily basis when I'm away from home and feel they're a great substitute for my Final D8000 Pro, when I can't or don't feel like using them. I use them mostly while at the computer, either at work or at home. They do a great job at putting me "in the zone" quickly in my coding sessions.
I feel they require a fairly high power to be loud. At work I plug them to a Lotoo Paw 6000, through a 4.4mm at high gain, and set the volume at 45-50. At home I plug them to a Burson Conductor 3XP, through a 3.5mm at high gain, and set the volume at 20.
The sound of these IEMs is so beefy it's almost tangible. To be fair, I feel my other IEM, a InEar ProMissionX (10 BA drivers), is slightly more detailed, however I feel the FATMSE are certainly sufficiently technical to give me a realistic impression of my music library. For example, it happened a few times that I turned my back to hear if a person was talking to me, when actually it was a voice from the music. In other words, the FATMSE may be "fat", but to me they're not "fatty", if it makes any sense.
The bass punches like nothing else I've heard before. I would compare it to the Final D8000 Pro, mutatis mutandis.
I hope this review helps you get an idea of my experience with the FATfreq Maestro SE. This is my first review, I kindly ask you to upvote or downvote it: it will help me understand if I'm doing a good job. Thanks and good luck with your purchasing decision.