I like the AC filters but..I looked at the design here
http://www.hagen.com/uk/aquatic/manual.cfm
I don't see any big issue with the design...it is MFG by the fine folks who mfg the AC filter.
the filter appears to provide mechanical and biological filtration..
depending on it's price it may be a good deal.
Another good option from what I've heard is like an AC 70 or a Rena Smart Filter, the new HOB Rena's and AC kind of eliminate much of the bypass that occurs with penguins and whispers.