Compatibility between the Markins Q20 adjustable lever clamp and RRS plates was a concern of mine before I recently purchased, but I went ahead on the advice of this forum. Very happy to report that the Markins adjustable clamp worked beautifully with two RRS L-brackets and a RRS replacement lens foot. The Markins clamp was factory-set a bit too narrow for the RRS brackets/feet, but the adjustment was quite simple and required backing a single screw out by maybe 1 or 1 1/2 turns from the factory setting. I was able to easily adjust it so the fit was snug, but without putting undue stress on the lever itself. There seems to have been plenty more width available in the adjustment if I had a wider plate to accomodate. I also reversed the clamp's lever action so that it feels more natural to me based on my old Manfrotto QR clamp (I now move the Markins lever to the right to tighten). The reversible clamp is a very nice feature for those of us who are set in our ways.
Both adjustments together took less than 10 seconds to accomplish. All that was required was a small slotted screwdriver, which I will keep in my tripod bag just in case any adjustments are required in the field. I shot for about 5 hours in freezing temps and had no problems at all with the clamp losing its grip, and I did switch cameras and landscape/portrait orientations quite a few times during the shoot. My clamp adjustment was made indoors, but there were no apparent changes in tolerances due to temperature-related expansion/contraction when shooting in the cold weather.
My only suggestion is that you should try to stick with the same brand/width of plate and not mix plate widths, in order to avoid having to re-set the adjustment screw in the field. It is a very simple adjustment, but I think it would get a little "old" if I had to re-adjust it every time I made a camera/lens change in the frezing cold. And I'd be up the creek without a paddle if I left my trusty screwdriver back home.
As of this writing, my equipment is all brand new:
Markins Q20 ballhead with Quick Release Lever RRS L-Bracket for D700 & D300 with MB-D10 Grip RRS L-Bracket for D300 w/o MB-D10 Grip RRS Replacement Foot for Nikkor 70-200mm VR (I or II)
Hope this helps assuage any concerns that others may have regarding compatibility between the adjustable Markins clamp and RRS brackets, plates, or feet. The combination works beautifully!