I think one needs to make a distinction between terminology and products. A digital phase converter can be many things, the ones sold on Amazon are no more than a static converter with maybe some digital controls, and it is a POS based on many reviews. RPC's have been used for many years, but not what I would call clean power for the third leg. Phase Perfect (PP) is clean power per their numbers and reviews, and the provided the cleanist power other then line 3 phase power, and there is tight regulation of the generated leg. Both an RPC and the PP pass through the L1 an L2 line voltages and only generate the third leg. On a RPC the third leg voltage can vary significantly. PP can be used on multiple machines within the power rating of the unit used, and can supply something like 10X is rated power for short periods for motor starting.
VFD is a different setup, it generates all three legs of power, but it does so in such a way (PWM) that it cannot run electronics/controls and is made to directly to the motor, as the coils smooth the wave form. Reliability, they all have long times before failure with little to o maintenance. VFD's these days have MTBF on the order of 20-30 years, this would also apply to the Phase Perfect. RPC is pretty simple, the better factory ones should also last a ling time. With the reduced price of the Phase Perfect, it would be my first choice, and also with older motors it would be the best option if one requires clean 3 phase power. VFD would be next due to compact size and relatively easy install, then RPC followed by a static converter.