I don't think I could watch a film on it, even a slight lip-sync problem would drive my crazy after a while. I could put up with it for short video clips though.
To be honest, I'm not entirely sure what the appeal is of watching a film on a tiny screen while streaming the sound to a hifi. Why not just just use earphones (or better still, watch it on the TV?). For me, this is all about streaming music.
Same issue with the M2, agree that streaming music is what it's all about.