I can verify that the man knows what he's doing. I bought into the Klipsch RP600M craze and unfortunately was left disappointed. Wish I would have caught Ron and New Record Day's review before purchasing. The shortfalls he described are exactly what I was hearing. Luckily he recommended Danny at GR Research and had an interesting comparison video trying to illustrate the difference before and after.
Picked up the upgrade from Danny. Skipped the tube connectors and instead kept the original binding posts. I took measurements before and after to verify that I had everything set up correctly. Sure enough the speakers measured flatter after the upgrade. The big valley between the woofer and tweeter was largely gone. The peaks in the tweeter we're smoothed out and response was nice and flat.
In the end I have a set of speakers that I can run without any sort of EQ and I am very happy with how they sound. Can't recommend his upgrades enough if there is something you're unhappy with in your current speakers and would rather not run EQ.
Only thing I don't find value in are things like tube connectors and special cables. If you're chasing that final 1% I could see it, but personally I'm okay with skipping that stuff. Not dismissing it, but I bet there are people who would be turned off by the way he pushes that stuff, especially when the whole measurements vs trusting your ears debate seems to be so heated lately.