This is a tricky looking exercise. As with parallel bar dips, you'll find that the triceps are involved in straightening the arm, however the positioning of the bar behind you throughout the movement eliminates virtually all involvement from the chest muscles and puts a lot of load on the lats, traps and rhomboids as you fight against the natural tendency to let the shoulders shrug up and keep the arms extended behind you at the bottom of the movement. Depending on how exactly you perform these, there'll be a fair amount of abdominal engagement in stabilising the midsection and at the top of the movement as well.
If you can do it without pain, power to you, but it looks to me like an almost 'needlessly exotic' version of a fairly classic exercise. If you've no access to parallel bars, straight bar dips aren't a bad option but it seems to be that positioning yourself in front of the bar rather than behind it is just going to put your shoulders under considerably more strain and, given how many people complain of shoulder problems when doing any kind of dips, I'd approach this with caution.