My wife runs a 20 gauge M2 for three gun. We shoot some pretty major matches (FN, Rockcastle pro am, Benelli shotgun championship) and she has never been for want of a 12 gauge. I've seen her clear Texas stars and spin spinners that other competitors had major problems with.
Its super light, super fast, low recoil and just plain feels good in your hands. She's had a lot of competitors both Male and Female stop to ask her if it s a 20 and to watch how it performs.
Its kind of funny when she hands it to the RO to get her pistol ready for a stage... first you get
holy shit this is light!, then they watch her shoot, then they ask if they can try is out after the match...
As for home defense #3 buck from a 20 is some pretty wicked stuff.