You get more freqs to choose from, more units operating simultaneously, and digital menus, outside of that, performance is same with M2 and M3, isn't it? All bells and whistles for the avg working band. I think rather than spending the money going from M2 to M3 you'd be WAY ahead using that money to get decent earbuds. For bass, you need good buds or you'll sound like crap in the IEMs, and hate your tone. That's my opinion.
Vocalists, guitars, can get away with cheaper buds, the tough thing to reproduce is low freqs that they don't care about.
Although, I've been using Atomic Bass earbuds, made for mp3 usage, not IEM, but they have awesome bass response, and still the vocals are coming out crystal clear. I'm sure UE TF10s sound better at $400, and you can find them on Ebay for $175. I was expecting to have to spring for them, I'm a bit of an audiophile. But the Atomic Bass have good isolation, good sound, and at $40 rather than $400, hard to justify even the $99 black Friday price for the UE TF10s.
Curious what about the M3 do you feel is so much better than the M2?
Randy