The ones from Fun Projects are the original "duplicate" of Ford's cutouts and fully backed by the maker John Regan, a avid antique automobile owner and electronics engineer. Some vendors sell a copy that they can't support and agree they are probably junk. John has repaired his at a modest cost even when the problem was caused by owner error.
For obvious reasons, John Regan's (Fun Projects) regulator design is proprietary. I will say that it contains a "fail safe" circuit that protects the generator should the battery lead become disconnected. And, it's auto resettable. If you follow the instructions and have a good generator to begin with, the VR will provide years of trouble free service for both. Plus, your battery will probably last longer too.