I actually find the car easier and smoother to drive with the M-Button engaged. Maybe this is because I'm more used to bigger NA cars where the throttle is more linear.
When I drive my car (which is remapped) around town, in and out of traffic, etc, I find it easier to drive the car smoothly with a little bit of throttle and M-Mode rather than no M-Mode and using more throttle. I guess it's just personal preference.
Having said this, I don't turn it on all of the time because I quite like having that extra "ooomph" available
