I have one of the old BlackHawk Omegas I've used the heck out of.
I always liked it, it kept my secondary clear and easily drawn past a vest (and all the junk on/in it) body armor, ect...
I did a class called "an interdiction to counter terrorism" from the sheriffs office ETR team a Looong time ago. The team commander greatly favored a vest mounted holster over the drop leg, he said adding the drop leg is just one more place on your body to get hung up on something rather than just having it on the vest that is already there. I can see that if you need to get into rappelling gear quick or something. But for me at 6'3" with long arms (he was 5'10ish) and lugging a 5" 1911 over their Glock 19s....vest mounted would be a bad plan for me, I guess unless it was cross draw?
If I ever buy another one though, It'll be a Safariland.