I'm currently with CATS, passed 10 so far, all first time. I'd echo what's been said already, one of the advantages of CATS is their flexibility. You can do their modules in any order or even chop them up to suit you. E.g. I'm doing 4 exam sittings, leaving 2 exams until the end in order to maximise ATPL validity.
CATS online product is not as good as BGS, but to be fair you get what you pay for. Their QB is not as extensive as the BGS 'ATPL Online' one, and yes virtually all CATS students use the BGS QB. I think it's fair to say every student regardless of their GS provider use Bristol QB!
The CATS brushups can be a little variable and compared to a friend's experience at BGS they do not seem as intensive. CATS do get in a range of tutors for different topics which is a plus.
The bottom line is the clue is in the title when it comes to distance learning. You have to have the discipline to do the reading and learn the subjects. No provider is a magic carpet to success. I have seen a couple who clearly did no work prior to the brush up week and were clearly hoping for miracles (which of course didn't happen).
Good luck with way!