This is what I'm getting at:
I currently have this QR plate mounted onto the underside of my K20:
With the RRS L-bracket, I'll have to remove the above QR plate to use it. Whenever I want to use it on a tripod with the cable release and assuming that the RRS bracket will live on my K20, it appears that I'll still have to loosen it in order to move it over to accomodate the cable release.
If I got the Acratech L-bracket, the QR plate that I have currently attached wouldn't need to be removed at all, as the camera will easily mount on and off of the L-bracket just as if I was mounting it directly onto the ballhead itself.
At any rate the QR
clamp on the ballhead wouldn't be affected at all.
I think what it boils down to in the end as to which one would work best for any given photographer is how much time s/he uses the camera on a tripod or monopod vs. handheld. If you find yourself using the tripod or monopod more often than not, the RRS bracket would most likely be your best bet. OTOH, if you don't use a tripod or monopod so much, then the Acratech bracket would work, for the ease of mounting and removing the camera from it.
Another thing to take into consideration is how often you tend to buy and sell bodies. If you have a tendency to buy a new body every time a new one comes out and sell the old one, then you could potentially save a lot of money over time by buying the universal bracket.
HTH,
Heather