Which QD Mounts have you tried? QD Cup is probably out of spec.
I've been a bit iffy on Sylvan's products. IIRC their first folder adapter was made in China.
Anyways they have improved, but it's hard to pass up the LAW especially when Brownells constantly does "Flash Sales" for $200
The LAW is steel, and actually has a NSN assigned to it. It's pretty damn heavy though.
According to Sylvan their adapter is 7075 aluminum. Great for light weight, but I'm skeptical on durability.