My experience with CATS was really positive. The notes are okay, but don't forget that not everyone thinks the same way so sometimes other books are useful as a reference to come at a concept in a different way. That's not dissing CATS notes, because I'd say the same for any school. I bought the CATS books in hard copy, am glad I did, and don't intend to sell them on because I want to keep them for reference. I did borrow a couple of Oxford CDs for Met and Engine stuff and occasionally borrowed Jepp notes on a couple of bits I was stuck on. Failing that, the instructor support was good.
The CATS app was really useful, although I haven't seen any updates to it do I don't know how compliant it is with the new exam structure / questions.
The CATS question bank wasn't the most user friendly, but on the more involved questions the explanations were very thorough. It's definitely worth using. I also used ATPLOnline mostly because of the way it remembers what you got wrong, allows you to revisit problem areas and keeps a record of what you've answered and your scores. The actual question content and explanations are reasonably similar to the CATS version.
Overall I would happily recommend CATS; they may not be as shiny as other schools, but the knowledge and expertise is just as good. With any distance learning course, the onus is on you to do the study, not the school to spoon feed you. On that basis, your results are down to you and not the school, so shiny bits are less important. You will get everything you need, without paying through the nose.