Fundamentally a VFD is a stop / start box. It just uses magic smoke hidden inside electronic package thingies instead of nice obvious contacts driven by a solenoid and has all sorts of other clever stuff inside too. (We'll not mention a manual that is not only large enough to be a serious drop hazard if picked up when not wearing hard toes boots but also a major threat to the sanity of any normal person trying to read it. Such are not normally considered advantages.)
Indeed the Eaton DE1 series VFD boxes are actually sold as a substitute for ordinary start stop boxes as being a simple way to get the usual VFD advantages of soft start and, if needed, speed setting. They require only the addition of simple switch controls to do basic motor stop / start, forward / reverse and, if needed, two speed duties. The internal parameters are preset to work fine on ordinary motor duties. Its claimed that any ordinary electrician can fit them with no special training. No display or buttons so they get hidden inside a cabinet. However if you look at the manual you find they are actually a full on VFD having all the bells and whistles inside which can be set-up in the usual way if you buy the programming widget.
Best thing to do with your Crabtree box now its fixed is to wrap it up and store safely ready to be re-fitted if the machine ever has to go back onto full fat three phase.
Clive.