So I was finally able to order the M2 wireless yesterday and received them today. I've had limited time with them, but here are some preliminary impressions:
1. They look and feel amazing out of the box. Really nice materials. I got the white ones.
2. These are my first ever wireless headphones. In the last few hours I've used them with my MacBook Pro at the office, with my iPhone 5S on the commute home including a train ride and walk / bike ride through central Amsterdam, and now on my iPad Air 2. Bluetooth connection has been flawless so far (knock on wood).
3. At first the ANC effect seemed quite mild compared to my Bose QC15 that I use when flying, but I noticed that I could keep the volume low on the train and still hear the music well. And the bike ride home was extremely dangerous as I really didn't hear any outside noise, so I'd say the ANC so far seems fairly decent.
4. Take this with a huge grain of salt, but so far I'm not blown away by the sound. It's too early to conclude anything, of course, as I need time for my brain to burn-in. There just hasn't been a 'wow moment' in terms of sound yet. Although I have great neutral headphones at home, my previous portables were M100s, which I have enjoyed despite the huge bass emphasis (they're pretty spacious and detailed sounding too). I'm certainly going to give myself some time to get used to the M2 signature.
5. I experimented briefly with listening to them wired, both with ANC on and off, and connected directly to the iPad Air 2 and through my Leckerton DAC/Amp. As others have mentioned, with ANC off there seems to be a slightly less even signature, with a bit more bass. They sound better on. In a very brief test I didn't sense a clear difference between wireless and wired (with ANC on), which surprised me.
Basically, first impressions are good, but these are very preliminary impressions. Thought I'd share, though, as I've been looking forward to these and am a little excited.