A Serpa is okay for a Glock or a Beretta 92 but avoid a Serpa 1911 holster:

http://www.youtube.com/watch?v=zYvAxLX6OzE

The Safariland ALS holster is vastly superior in every way to the Serpa. It is a LOT easier to draw from with the support hand. I've seen some scary looking stuff go on watching support hand draws from a Serpa.