SEIOs are 4-pole (at least, although there is no need for more than this) motors to enable the motor to start in the same direction every time. This is also why they are so chunky in comparison to say, a MJ of the same wattage. Most other powerheads are 2-pole. This is why SEIOs are more $$$ to make, and this is also the reason that the controller will work on SEIOs but might not work as well, if at all, on other powerheads.
It depends on what method they use to slow the pumps. If they are able to manipulate the Hz clock cycle, as mentioned before, that means not only more electricity is used the slower you go, but more heat at the motor. If they block the AC current in a sine-wave pattern (this is how ceiling fans, oscillating desk and box fans, etc do it) it would be a much better result, and also require a 4-pole motor or else the motor would run the chance of changing direction at lower speeds...meaning rattling and seizing of the motor.
RichConley is right on one thing though...there is no evidence or scientific reason why these things wouldnt work on other powerheads...as there is no evidence at all. But the internal structure of the motor is different than your average powerhead...and I think I know why...