although I haven't had a rotary phase converter, so no experience there.
I got a used millrite a while back, which came with a 3 phase motor. So I had to do something to power it up and the vfd is a pretty easy solution. Its relatively affordable, and if you are into finer tuning your equipment, most vfd's allow for lots of programming options.
I just use mine for the conversion to 3 phase and for speed control. That is, you can change speeds on your machine, within a reasonable range, simply by pushing buttons on the vfd. Way easier than changing belts or gears.
Pacific Airgun Expo