Like several posters above I studied with CATS in 2008 , not for the PPL but for the IR TK.
Along with a dozen or so pilots from another forum we negotiated a discount for the course material with distance learning and CATS arranged weekend refreshers at Cranfield where they were based, as most of us were working full-time.
I was one who needed one-to-one from Stuart Smith on one knotty topic and his time was freely given. Nothing was too much bother.
I think the CATS material was perfectly sufficient for the IR, though I did buy a set question bank- German origin, 'Peters' I think as well. However this was studded with unnecessary ATPL questions so I binned it early on.
For the 7 IR exams I passed all first time, my average score was just under 94%.in a total of five months part-time study.
If the PPL is half as good as this I'd strongly recommend CATS.
Cusco