I recently installed Fidelizer Pro.
I have an i7 NUC in a fanless Akasa case powered by a Fidelizer PSU, running Roon Server on Windows 11, connecting via USB to Matrix X-SPDIF 3 and then via IIS into a Matrix DAC.This combination is the best digital source I have used. It has beaten some vastly more expensive "audiophile" servers, streamers and DACs that I have used in the past.
My plan was to use the NUC as a Roon Server for my very expensive streamer, and then into the DAC. But I found the NUC directly into the DAC (via the X SPDIF 3) sounded best, without the streamer.
The Fidelizer PSU on the server made a noticeable improvement, so I thought I would try Fidelizer Pro. I haven't done extensive comparisons but I found I preferred the sound without Fidelizer Pro, which sounded a little thinner, a little more clinical. Roon on Windows 11 without enhancements sounded more natural and fuller to me.
This is with the qualification that in my experience different software and hardware configurations can sound completely different depending on the specific set up. What works well in one configuration can sound worse in another, and it is almost impossible to predict what will work or not. Fidelizer Pro may well work well in other set ups, so my non-scientific impressions should be taken with a grain of salt. The cost of Fidelizer Pro is relatively tiny compared to the rest of your system so I certainly wouldn't discourage you from experimenting.