I used an RRS lever clamp for a short while long ago (shortly after the lever design came out, if memory serves). (We needed a new support system at work for some product photography and I convinced them to get this gear.) I had heard that only certain plates were compatible, so gave it a shot. Of course, the RRS plates fit just fine. I have an old Arca-Swiss brand "universal" plate that fit just fine, too. I also had an old Kirk plate -- which had seen lots of use and some of the anodized black was wearing off -- and that plate fit differently. It didn't clamp quite as tightly, however it seemed a perfectly fine tight to me. There was no movement to it, but when pushing the lever to clamp, it closed just a little easier.

FWIW, I have an AS B1 (screw-type clamp) and I always thought I wanted a lever clamp because it would be faster and easier to use. I didn't dislike the screw system, and it really is fast to use by sliding the plate in through the side and turning screw knob about a half turn. I was wrong, in that I didn't find the lever to be any faster or easier to use, and since the screw knob doesn't leave me with the fear that I may accidentally pull the lever, it's the system I prefer.