Personally I love the M button.
Just got home now, on the way some guy in his Porch Carrera "Cabrio"appeared in front of me. First reaction was to hit the M (full attck mode
) button and sit close, then blast past him. I know my number plates are wanky (M THREE) but come on why would you have PLAYER (unless you are a wanker!)
As other(s) have said I have both a 135 and and M and love it just the way it is, EDC and M Mode. If I were buying an E90 I would option it, purely because it is an incremental cost increase as an option but would, IMO, make it more re saleable down the road and, in the mean time, you can make use of it whilst having some fun bouncing along with the EDC on Sport (bounce bounce bounce).