The piton brake bar is very similar to a Pitt Stop. I don't have a picture of the piton brake bar, but it is just a piton clipped on to a screw-gate carabiner, with the rope running over the piton and under the carabiner.
Safe The piton brake bar cross loads the carabiner gate quite a lot, due to its small size, and this is the weakest point of the carabiner
Quick release Very quick
In line Yes
Light weight Yes
Variable speed Not easily. Using a smaller or large carabiner can change the speed, but this takes time to set up.
Variable speed during descent No
Easy to lock off Not particularly
Rescue use Poor. Adding an extra person would be inadvisable
Belay use No
Heat dissipation Below average