The AR-1 works well on the Nikon Rf's. On the SLR's you still hve a problem with mirror-slap (unless you put the camera on mirror lock up). Only problem is that it is very tall and if you bang the camera against something it puts pressure sideways in the release collar. The good thing is that the Nikon's collar is sturdy enough to take it.
Very handy on S2's if you use a bright line finder or VC meter on top of the camera as it moves the release "up" a bit and less chance of getting the finger tangled up in accessories!
There is a clone of these made in Japan, picked some up a couple of years ago and, though still a bit tall, they work well.
I have been playing around with a design for it that would be spring-loaded and slightly lower - but so far no prototypes. A bit complex as it would require 5 different parts (collar, lock-ring, release button, spring and a complex shaft to hold the spring) which would make it quite expensive to make.