Besides the issue of the locking mechanism, there's the controversy of AD when drawing from a Serpa:
http://www.youtube.com/watch?feature...&v=XTGmTrQXrwg
What? You asked for our opinion... lol
I'm personally not a fan of any mechanical retention holster at all. If there are moving parts, there is chance for failure. Period.
Some designs are a bit better at clearing (or preventing) obstructions than others. I won't get in to that debate - I'll leave it up to you to decide. But for what it's worth, I've personally decided to go with Safariland SLS for my drop leg thigh rigs, despite my concerns about mechanical holsters...
If you want tacticool, Serpa is sooOooOOoo 2007... Kydex holsters like Raven Concealment's products are the new tactical Gucci