I have a Hejnar converted 410 and it is a very elegant and efficient solution, much more so than the Kirk 1 inch clamp attached to the Manfrotto 410PL plate I have fitted to my 405 head.
Hi,
I have the Hejnar adaptor on my now modified Manfrotto 405 Pro geared head, and that works fine with the rest of my RRS accessories. I also got his clamp, and that works fine as well (finishing is not as smooth as an original RRS clamp, but it functions just fine).
Cheers,
Bart