They are not true multi-motor converters. Roto-Phase, being a rotary type, is a three phase distribution system in which a variety of motors can be operated individually or simultaneously, just as though connected to a three phase line. As Roto-Phase is rotating, a phase shift is accomplished through a rotor spinning within an electrical field. The result is a true three phase. Performance substantially exceeds that of all static phase converters a comparison is almost unrealistic.
Some static types can give a reasonable performance, but even they are limited in comparison.
The reasons are manyfold. No static converter can make all of the above claims. Plus, a number of motors are operated while the static types are generally confined to one motor. Roto-Phase is a manufactured device that comes closest to a solid three phase line. Against other solid three phase systems the Roto-Phase is merely the best substitute.