I own one. I use the four big vertical foam blocks because you have to, and ceramic rings in trays. Rings because bioballs don't really fit.Sometimes some floss in the top tray if I need to scrub the water.
Good: solid constuction of filter canister and latches, incorporated shutoff/disconnects, quiet.
Bad: Cheesy proprietary grey tubing that clogs easy and stands out in the tank, water path that allows only a couple of media configurations, small media trays, IMO - cheesy inputs and outputs.
I love my Rena filstars. But, in general the Fluval is a good filter. I have not experienced a problem related to workmanship or quality.