I have a PennPlax Cascade 300. I bought it because I needed a filter in a hurry and the store that sells Aqua Clear was closed. This filter is supposed to be able to handle a 100 gallon tank, but I would not trust it to handle even a lightly stocked 100 gal. It is a good filter for my 55 gal. piranha tank, and for $40 I think it was a good value.
Bottom line, good value for the money, with some drawbacks. It's a little noisy, I think it should move more water, filters well, does not lose siphon, cartridges are cheap (3 for $10). I would not buy another one except in an emergency. I'll stick with the AC's.