Mag cost aside, operating with 10-rounders is good reason to train "speed reload" & "tactical reload" skills with multiple mags. A discipline that is transferable to centerfire PCCs and pistols. No recharge, avoid unspent ammo, steady discharge rate across multiple mags, muscle memory. Whereas, if the 30-rounders were available such skills might not be considered valuable to master and the fun of tactical mag management could be missed?!?