Not a Serpa fan, too many experienced shooters have shot themselves in the leg trying to operate that holster under stress.
Top Shot Season 1 runner up Chris Cerino a Law Enforcement trainer is the latest victim of the Serpa that I'm aware of. You can read about it here Firearms instructor accidentally shot himself ETA:Reported to be Chris Cerino of Top Shot fame - Page 1 - AR15.COM

I think the Safariland ALS series of holsters is a far superior choice. The 6377 would be a good choice.