My brother used them. Said he'd never run a flat tappet cam without them again.
He said they tame wild cams a little bit down low and then pump hard like they are supposed to do up high. Makes it more driving friendly from what I'm told.
I ran them on the first motor I built. It was a 292* .525 lift cam in a 70 302. It had terrible idle qualities and low end was less than desirable with standard hydraulic lifters. I installed the Rhodes lifters and immediately had more vacuum and low end punch.
I have a brand new set for sale if you are interested. No, the above was not a sales pitch.