I went to try a horse for loan, an 11yo warmblood, and he was in a snaffle with enormous keys. The owner said she thinks he likes to have something large in his mouth to "hold on to" - this is weird, no? Would you happily ride in a bit with keys long term? The horse did not crunch them as a youngster would. He tended to overbend and was a little resistant in downward transitions and that was even with me trying very hard to be light handed. I am thinking of asking to get his teeth checked.
Well its just a straight bar, so it wont have much wellie for slowing down. If he responds to it nicely, then there cant be much wrong with him. I dont think that being totally rideable in a training bit is a bad thing. The over bent thing could be down to being lashed into training aids and having set that way.