You can sit the exams in however many sittings (within the limits) you like, there were people on my Mod 1 brush up who split their exams up into 2 sittings. I have a feeling Bristol may also, if you phoned up and spoke to the girls on the desk, be able to sort you out with a brush up on the subjects you want to sit alone, without you having to sit in on the others (provided its not a mix of Mod 1 and Mod 2 subjects which may clash on the timetables).
As for CATS I've never dealt with them personally, but I've certainly never heard anything bad about them.
Good Luck.
Last edited by packo1848; 3rd Jan 2013 at 17:20.