The Roto phase it great for something like filling a cistern. It is not good for a pressure switch control because the Rotophase has to get started a couple of seconds before the pump starts. Add-a-phase with the capacitors works very well also as long as the demand or amperage stays the same as it does when just filling a cistern. Either one of them will be more reliable than a Subdrive. However, it might be less expensive and would last longer to just switch out to a single phase motor and up the wire size if needed. Standard single phase pumps filling a cistern should last 30-40 years. If they had installed a regular single phase motor and proper wire size to start with it would have been much less expensive in the long run. However, being more expensive in the long run is why many installers push those variable speed pumps or VFD's.
