I put Pierce extensions on the 9 rnd mags for my XDSC almost as soon as I bought it.They don't stick out enough to change the way my XD patterns and make a big difference in making my grip more secure and consistent.
I recommend them highly.
I just got a Pearce pinky extension for my XD .40 subcompact and it's the best of both worlds (a fullsize-ish grip without extending the handle). Springfield maybe should have just included something similar with the smaller mag to begin with. In any event it's the perfect accessory unless you have small hands.