I totally agree with the other comments made here and although I didn't make it past stage 2, I got so much out of the day through speaking to fellow wannabes and the informal, knowledgable staff.
Just a minor point, which may or may not be of use, but the computer programme now being used for the tests is PILAPT, not COMPASS. The only significant difference really being that the use of foot pedals has been scrapped and it's mainly a hand-eye coordination, multi-tasking, spacial & aritmetic set of tests.
Just be yourself and enjoy!