I gotta say, that I agree 100% on CQBs product, I love my UM-84 leg drop holster kit.
If you've got an old military flap holster laying around, this kit is the stuff, but be sure to get the new 2 strap model as they would seem to hug the holster tighter to your leg, still I like my older, single strap model, just fine.
Very well made gear at an affordable price.
I wish they would make a modular leg drop panel for the other leg. I've been toying with the idea of buying a modular leg drop and rigging it to fit over my cheepo Tac Force 100 oz hydration bag (Kind of like a CamelBack Thermoback, with better shoulderstraps and a pouch on bottom.) then I could switch out pouches on the top of my hydration system or take it off, to use as a leg drop if needed.
I,ve also considered Blackhawk's drop leg medical bag for the "bag attached to the top of my hydration system" role, as it has lots of interior pockets and velcro straps to hold all manner of small gear.