I bought two of these for under $40 total and decided to play around with them to see what could be done about combining them.
Since they are slightly larger at the top than at the bottom, stacking them would not work; instead, I used my Dremmel to cut the bottom portion of one of the tops free. Then using the sanding features, I was able to remove a portion of the ridges inside the band, so that I could fit the adjusted end over the top of the other unit. It ended up being a sleeve to combine the tops. With a little underwater tape, the middle was set. I also took sponge out of the "top bottom," and in its place I put some underwater tape fashioned into a little cap with a portion of it cut out (to lead the bubbles into one spot). I cut the bottom sponge in half, too, to increase the inflow.
Then with the media inside, I connected the bottom air hose attachment to a fairly strong air pump, and with some air hose, I attached the top air hose attachment to the aerator insertion point of the outflow of a surface skimmer. This way, the skimmer's powerhead pulled a current out of the top of the "top bottom." The result has been nice! The water is only a bit cloudy now because of all the aeration from another power head. The water is very clear and mature, the corydoras' barbels are long (meaning, no nitrates), and the tank just seems healthier.
It's not the prettiest set up, but for the price, it is really functional (the plants hide it from the front, anyway).
These fluidized filters really do the job and at half the price that I would have had to pay for one as big. I do recommend this unit, as its simplicity and appearance both are more than adequate for the price.