Just installed the M gear knob in my F20 118D and put it on youtube:
Quite easy to install, just pull the leather wrap-around away from it by pressing the sides. Then pull the gear knob with a lot of pressure untill it pops (mind your head!). Replace it. Then pull it firmly down till you feel it popping in.
Happy with it, but it is not a shortshifter as my old E87 118i M-sport had, it is still a bit higher. Visited a BMW dealer in Amsterdam and saw an F20 M-sport but noticed it having not a really short shifter. Too bad.