Stillpoints Ultra 6 vs Critical Mass Center Stage 2

Hello, I am about to pull the trigger on a set of four to place under my amp. A dealer senT me a set of stillpoints ultra ss to try under my new dac and the results were amazing instantaneously. I love that it is so easy to test as well. I am now a firm believer in isolation footers.

I would like anyone who has any experience in these two products mentioned as it seems they are the two best options. Ideally, if anyone has done an a/b comparison it would be really helpful to hear your experience because they are far from cheap..! Thanks for any input.
Cheers!