The impeller on a whisper 60 is a magnetic drive impeller, basically there is no physical connection between the motor and impeller. So if it stops no damage is done to ether the impeller or the motor. The magnetic energy / field is simply lost. The only real fear on this type of a design is no water being present around the impeller to balance it and to keep it from touching anything while it spins. I don't know about most, but I would suspect a good deal of HOB
filters work this way. Plus this filter has a flow control that works by opening and closing portions of the intake.
I got this idea from looking at the Aqua line of filters that you can change the filter setup. And mimicking that setup to a point. From what I've seen the filter could probably hold 3 filter cartages on each side without stuffing. The second would fit fairly easily. The floss cartages for this filter are thin and not very restrictive by design.
Oh yea, Mods if yea see this could you move this to equipment area?