They don't really follow either IPSC or IDPA. There are quite a few current and former IPSC shooters who shoot there, but no speed holsters allowed. Everything is geared towards real world operations.
Every course of fire starts from a draw. OSA does their own holster qualification so you don't need Black Badge or any other formal holster training. There was moving targets, shooting while moving, barricade work, 50m, ground work (shooting from knee, back, and laying on your side) mandatory mag changes.... I know I'm missing a bunch, but that's all I can remember off the top of my head.
Pistol requirements are "anything that you would realistically use on an operation" Most people there seem to shoot .40 or .45 but a few people use 9mm. They'll let you run with .22lr, but you'll be penalized for it. Scoring for the OPC is based on accuracy, not speed, but there are time limits for each course of fire.
There's usually at least a handful of LEOs out there for the match and a couple of military types as well.
They usually run a skills and drills course the week prior to the competition, which I wish I had done. They go over all the skills you'll need for the competition. If you have experience with IPSC or IDPA you would probably be fine, but I was a newbie to that sort of shooting, so I was a bit overwhelmed by the competition.
I really enjoyed it. Definitely something I'd like to do again.