i went to scheel's today and tried a serpa (made for the glock 20/21/and something else) today on one of the store's glock 30SF's... and not to bash your thoughts rrc, but the holster constantly took the gun out of battery everytime i holstered it, it fit very very snug (too snug to easily draw, required far to much effort) and it bothered me to the point i ended up getting a fobus paddle for it... least i got a range holster for it that will work...
maybe just a freak accident that wouldn't have happened with another serpa 21 holster on the shelf (maybe too tight or something) but i figured i would post my experience with it...