From what I've heard the lead sleds are great for sighting in and getting accuracy results with less punishment on the shooter. The problem as I've heard is putting too much weight (like the 100 lbs of lead shot in the advertisement) on the sled. With the heavy weight, upon firing of the weapon, the sled does not move, but the energy has to go somewhere. So it goes back into the rifle and cracks stocks and I would probably say adds undue stress to the optics.
If you're recoil shy and do a lot of load testing I would say go and get one but only put 25 or 50 lbs of weight on it.