I have one - think it's Hagen too, but can't remember.
I thought it would be a novel little gadget - well it was a waste of money.
Unless you have plecs that poop a heck of a lot on sand, and would just like to "hoover" every other day to make the sand look clean; I guess it's OK.
For gravel tanks and/or light/medium level waste fish, I definitely wouldn't bother getting one.
But you'd still need to do your weekly water changes.