I am a fan of the RPC. I know there are lots of good options with the VFD, like speed changes, but you need one for each piece of 3-phase equipment you end up with. A good RPC can be wired into a sub panel and you can wire the entire shop for 3-phase off one unit. The other advantage, at least for me, is that you just plug in your three phase equipment and run it. Nothing to rewire, or bypass or program. You get full power. All the control circuits and switches work like it came from the factory. If you have other motors on your equipment like coolant pumps they do not need to be changed out. Old three phase motors are cheap and can be wired to a phase converter panel. Several companies sell just panels.