You also get debriefed one on one with the GAPAN tests and they have no interest in it other than to make you realise if you have the aptitude or not. OAA on the otherhand will be making a very healthy profit out of you should you meet a minimum requirement.
Yup, and as far as I know, it tests aptitude in a a way that you can't cram or revise for. You've either "got it" or you haven't.
Not been to an OAA open day, but wonder what you have to do pass. I mean, someone with ab-initio requirements (i.e. NO flying experience) almost by definition should screw up anything they try to do in a simulator, so why do it? there'll be more boring, but easier to interpret methods of assessing hand-eye, depth perception, decision making, reaction times etc. etc.
Also, maths is maths whatever you're applying it to, and a reasonable 'A' level maths student should be able to handle most things thrown at them.
At the end of GAPAN, you get 1-to-1 with someone in the industry for feedback/ advice etc. To my knowledge they don't get paid for it whatever you decide, so maybe a bit more impartial?