I didn't really care for it to be honest. It just wasn't comfortable to me when shooting and I actually preferred the original grip. Having said that, it did make holding the camera via the grip easier. But the bigger factor for me was comfort while shooting.
I realize I'm in the SMALL minority with that opinion and if you've used one of his grips before and liked it, I can't see why you wouldn't like the grip for the M.
We had an expensive drop with the s90, so it was important to me to have the extra secure handling. The thing is, the M body is thicker, so the shutter is farther back from the other fingers which is not ideal.