Since the Nikon collar does not have an Arca Swiss dovetail, I initially screwed a dovetail on the Nikon collar.
When Kirk announced their collar, I contacted RRS to see if you were going to make one and they said no. I bought the Kirk collar. It balances perfectly, but doesn't rotate very smoothly and the attachment screw is not captive and seems to want to fly off on removal. I, consequently, tend to leave it on the lens, even when hand holding. It's also a one piece design and bulky for travel.
RRS subsequently changed their mind. Noting the deficiencies of the Kirk, I bought the RRS. Unfortunately while it has none of the Kirk collar flaws, it has one of it's own. It doesn't balance with the lens at 500mm on either a D500 or D810, even with RRS L-Brackets. RRS acknowledge they knew of the problem but weren't going to do anything.
I really wanted the RRS to work because it's easy to remove and stows very small, but not balance is a critical flaw and I returned mine. Shame on RRS for such shoddy design work and lack of testing.
pictureted at flickr