When you pull back that second bar is going to put pressure under the jaw, kind of like a curb chain.
I am pretty relieved actually, I grew up riding western horses and what was referred to there as a bumper bit was a mullenish mouthpiece with a steel curb piece, not a chain, and it was a pretty vicious bit. I would never, ever put one in a jumper's mouth. I rode in one a time or two back in the day under instruction but it was too severe for me, the horses cowed behind them. Not something I'd ever use again now that I'm not 12 and am willing to say no to trainers.
But this one might be a pretty strong bit too, come to think of it. It might not be steel but it is one piece. Nathe is pretty soft though, it might be OK. Not something I'd spend $300 to try unless I could borrow it first.