Never used Atarnotes stuff, did use checkpoints and A+ note exam booklets tho. So here's what i think of them:
The checkpoints books i actually used provided good, tough questions. My only issue is that some of those 'tough' questions were from past exams, which impacted my exam prep. This was only because i remembered most of the answers to the more time consuming ones which made me finish earlier. (I had to give up on the 2012 Methods CAS exam half way in because 3 of the 4 questions in section B i did in the checkpoints book.)
A+ notes are useful cause their regular practice exams, and in some cases have practice tests for specific areas of study (which is useful for preparing for SACs) but i myself didn't use them as much as i probably should've.
Another thing to beware of is that these books won't be counterproductive. I gave up with the Physics checkpoints book and the Chemistry A+ book because their questions and explanations were so awkward for me that they ended up stressing me out. If you know a mate who is buying one of these i'd suggest borrowing it from them and doing some question first before buying anything.
Honestly, they both helped me fine, but i personally preferred the A+ books. To be fair, i only started to actually use any of them about a month or so before my exams, rather than consistently throughout the year.