Comparing the M2 to the MTW without sound comparison while the MTWs charge:
1. Case. Earin clearly wins. The case is about 1/3 longer, but the round cylinder form factor is really nice - easier to find space for. Plus the MTW has all those well-documented charging "quirks and features" (to quote Doug DeMuro) that make it unreliable. The Earin case just seems better all around - I like the machined aluminum look better than the burlap thing, the whole "cradle" thing seems better engineered than the simple holes on the MTW case, there are 3 lights to indicate charge on the case and separate ones on the inside for each IEM, on and on.
The MTW has USBC, which is a big plus. And the Earin magnetic bottom is concerning. The MTW case is also magnetic enough to hold a paperclip near the clasp, but I think that's less likely to come in contact with something problematic than the entire quarter-sized bottom of the Earin case's cylinder. But those are the only advantages on the case.
2. Fit/finish of IEMs. The Earins are tiny. In fact, this makes them a bit hard to fit properly compared to the MTWs, which go into my ears perfectly as if made for them. You can put the M2s in wrong pretty easily because they fit anywhere. I can see that for some people that would be an advantage - I can't see anyone having fit problems with these like the problems I have had with the E8. The M2s also seem more "high-tech" due to the size and shape - it just make them look less plasticky and more advanced. Both are light (they feel about the same to my hands), but the lightness of the MTW combined with the plain matte black plastic makes them seem a little cheap in comparison.
3. App. The Earin app is weird. It has "gain" - which is just volume and thus kind of useless (just use the buttons on the phone) and balance but no EQ. It also only tells you the power level of the master IEM, not both, and does so by filling up a circle rather than giving you a percentage. The presentation is incredibly minimalistic and "homemade" looking - you either like that or not. The transparency setting part is fantastic, though it has a volume adjustment for the ambient sound, as well as a "Near/Far" adjustment. It also allows you to use it in "Auto" where it automatically engages when the music stops but is otherwise off. The "Near/Far" thing is amazing - I can talk to my wife but still not hear the TV (or vice-versa!

).
The MTW app has an EQ. It's kind of goofy but better than nothing. But transparency is wonky (never got it to work while music plays) and the battery levels engender angst due to their granularity.
4. Connection. MTW is rock-solid. I've never had a drop or cutout. Never had an issue connecting to phone or app. Just put them in and hear "connected." It's kind of cumbersome to switch devices if both are in the same room (have to put them in pairing mode and pair with the second device each time), but other than that this aspect is really solid.
Earin's connection process is a PITA. Horrible. The app needs to see each IEM connected separately to work. But when the IEMs are running only one or the other is "connected" to the phone and the other is a "slave." Thus if either one is out of the case, the phone connects to that one and disconnects from the other one. So I can only get the app to work when both the IEMs are in the case - the only time I can connect both to the phone. The IEMs themselves work fine, but if I want to use transparency mode or balance I have to put them in the case, open the app, then remove them from the case with the app running. Then if I switch out of the app and back in I have to restart the whole process. Thank goodness I didn't have to update the firmware. I haven't even tried connecting them to a second device - the thought exhausts me.
More once the MTWs are charged up.