I have the one that accepts the ARs
It's great.. I take it to the range and use a wagon (hey, i have kids and more stuff to haul to the benches to shoot than hands)
I take the sled and use a couple of bags of lead shot to hold it down..
I like it for load development and scope zeroing.
It just holds the gun super steady, and removes all shotting veriables and as long as the wind isn't blowing, i know if the groups are good or not.
It's also great for zeroing and usually only uses 2 shots.
I set the sked and have the gun in tight, bore sight. I then make sure the scope is pointing right at the center of the target. I then fire off the first round, and then reset the gun and re-align the scope to center. Find the hole from the shot, and then turn the knobs until it's lined up on the hole from the first shot.
Readjust gun to point at center of the target and fire again. Usually dead on. But some small adjustments may be neccessary.