A Penductor and Eductor work basically the same way. A Penductor is a little bit smaller though. It works a lot like a venturi actually. Basically what happens is the water coming out of the pump is restricted to a small opening thus increasing the velocity of the water. With the increased velocity, a low pressure area is created and the surrounding water is sucked in as well. It is supposedly able to increase the flow from an outlet by 5x or so. Therefore, even with a smaller pump (say only pumping out 800GPH per outlet), you could theoretically get it up to 4000GPH/outlet with the use of an eductor.
Unfortunately, this process created quite a bit of back pressure, so you'll most likely need a good pressure rated pump to use the optimally. The eductors themselves are quite bulky as well.
As for the Penductor, iirc, littlesilvermax on the forum here uses them on his tank with an OM 4-way, so I'd hit him up for some "real world" impressions of it.
Here is a link with much more info:
http://www.reefcentral.com/forums/sh...hreadid=372881