Thanks for reporting back on them, Seaice. Interesting results, does that mean the iPurifier is out and moving onto the For Sale forums? If so, I do have an open Wanted Ad for one and would love to have a listen to it if so.
As for the results, do you still find that with the two in tandem, PC>USB cable>Short Block>iPurifier>M7 (as you originally had), that the results are different and better than just the Short Block alone?
The Ultra Fi Aubisque USB Filter was the first USB filter to mention filtering the data/signal line (like the iPurifier now says) and not just cut the +5v line (like the Short Block does), so that one is first on my list to try. It's just a real pain trying to find one on the used market. I had my head down for a bit and missed one that was on Canuck Audio Mart 2 months ago :-(
My review is still ongoing. I will assess the tandem later and let you know my results then. I am not sure about the "For Sale" forums now but the Short Block stays for sure.
(By the way, I believe that the Short Block is more than a 5V line cut.)