Do the RMAA loopback test. Run the test three or four times with and without fidelizer. If you get the same results with and without fidelizer then you know you're having yourself on.
I've fooled myself when I expected or wanted to hear a difference from something, and then actually measured the results.... no change!
If fidelizer is actually doing something, you'll get different results from the loopback with and without it. If you don't get different results, then you know your expectation bias has led to you fooling yourself.
Frankly, the guy who makes fidelizer is a bit nuts, a bit of a fraud, or a bit of both.
Look at post number 369 on this page:
Somebody pointed out what I mentioned about his diffmaker test being faulty, because he uses a software loopback that isn't bit perfect. The guy calling him out then makes a bit perfect recording connecting a digital spdif output back to a digital spdif input. Perfect null. No fidelizer used.
You've been had. Your money taken in return for snake oil.