I've never heard of anyone being hurt by the bushhog flipping up and hitting them from behind because they use a chain instead of a top link. I must admist that I am biased, because for the most part, I use a chain instead of a top link. It seems that my bushhogs are fairly heavy pieces of equipment, and even though they carry alot of power, they are really going to have to hit something really hard, really strangely to make them bounce up more than 90 degrees. I would also think that the PTO shaft, even with it's U-joints, would also discourage the bushhog from trying to sit in my lap.
On a related note, both of my Howse bushhogs have fairly long slots on them where the top link fits in. I had an older economy cutter (can't remember the name) on another Yanmar tractor that had an A-frame on the front that flexed at the bottom pins and there was a bar with about 12-18" of chain on the end of it that ran from the top link hole to the tail wheel of the bushhog, giving quite a bit of flexibility.
Take it Easy
Tim Gray