My understanding is the CAT exam format has had no bearing on the recommended study materials.
My advice, try to get the latest material you can, look for a large number of good rating on Amazon with a recent publication date. 'All in One' or ISC2 Official Study guide are both good and I think about thirty/forty USD. One is enough, though no harm in both if you have the time to invest.
CBK will change periodically and new exam questions will be added, but I would not expect it to hugely impactful. Even the refactoring of the ten domains into eight didn't really change the content in the CBK.
One thing to be aware of the new format effectively penalizes wrong answers, so pace yourself well.
I want to preface my reply by using the popular acronym, YMMV!
My core books were the Syngress CISSP Study Guide 3rd Edition (Conrad) and the Sybex Official Study Guide 7th Edition (Stewart).
My secondary references (when I wanted to get a deeper/clearer understanding of a concept, especially when I got a practice question wrong) were (in order of liking): Official Guide to the CBK 4th Edition and the ubiquitous All-in-One Guide 7th Edition by Shon Harris (RIP).
People have commented that the CBK is dry, dry, dry 🙂 I personally found it to be a more engaging read…BUT WARNING…the index was...to put it delicately...sub-par at best; hope the 5th Edition will improve on that aspect. Personally, I bought but did NOT read Shon Harris’ book apart from the occasional cross-check (I know some of you fainted right there because you've heard it time and time again referred to as THE study resource) …it is WAY TOO DEEP for the exam (in my opinion), BUT it IS an excellent on-the-job reference.
I am a fan of multiple references for at least two reasons. 1) Sometimes you read a concept in one book and you don't "get" it. By reading the same concept in another book, you it may be explained in a way that makes more sense to you or provides some added depth you need tom make the concept "stick". 2) I get bored easily and it's nice to flip between "voices" when reading what can sometimes be dry material. #my2cents #ymmv