The Roto-Phase is a motor/generator which creates a 3rd phase through it's rotation. They work quite well for years without problems, but that being said Reno is right, the VFD is a much better product especially if you are on any sort of demand charge billing. The price of VFD's is good and they are readily available. I would install the VFD.
That being said, I have many 20 plus year old Roto-Phase sites that just keep plugging along and they will not be replaced until something dies.
I recommend TVSS protection on either installation.
