What is this "Arca Style Clamp"? It has a funny looking protrusion on it (I suppose this has to do with the lens ring mounting?). Despite it's presence, is it still possible to mount a normal dovetail nodal rail on this? I'm looking at the RS-2 as an Arca plate alternative to the NN4 (or upgrading a NN3 using the conversion kit). What concerns me is the upper clamp. I'm also eying the Ultimate M1-S, but the size and weight is a bit much and its' overkill for my needs.
Any other way of getting a NN3/NN4 sized head with an Arca upper clamp would be perfect for my needs.