Yeah, the range that the controller varies the power to the pumps (30%-100%) would most likely be 100% all the time to the 620 and 820 since they are so small.
The controller 'might' work with other powerheads according to Taam. The problem with most other powerheads is prolly going to be two things, if these controllers are designed the way I think they are (by manipulating the frequency)...
One thing is how many poles the AC motor has. Most powerheads only have a 2-pole design... the impeller can rotate in either direction upon startup. I believe the SEIOs are a 4-pole design... 4-poles allows the motor direction to be controlled, which is necessary to the SEIO's operation. While ramping down the power on a SEIO, the 4-pole design allows the pump to continue to operate... but with 2-pole designs (Maxi Jets, Aqua Clears, etc) the lower power could cause the pumps to switch direction and 'sputter' depending on how low the torque of the powerhead is in the 'off' phase.
The other problem is the size of the motor. For the same reason 620s and 820s wont work, if you use some similarly powered powerheads (like a MJ 400-900), the output might not go low enough to cause the pump to vary anything noticable. The wattage of the 1100 (15 watts) on up suggests that you will most likely only be able to get this controller to work on larger powerheads... perhaps the MJ1200 being the smallest, along with the Aquaclear 802. Pretty much only powerheads that are 15 watts on up...
At least, thats my guess. Trial and error seems to be what SEIO is suggesting to do here... perhaps someone with one would be so kind as to plug in a MJ1200 (or similar) and let us know....??? (PETERSEN 'cough' 'cough')...
