I used to use cellpore (both in Emp 400 and assorted AquaClears). They will eventually clog and you cant really unclog them- threw out my unused ones also and went back to sponges.
I got 4 of the fostersmith carts to try them. I dont use the white carbon filled pads. Instead I cut a rigid type of floss to fit in them and replace it weekly. They are a tad on the flimsy side but work. I dont like the Emp. gray media carts as they are a PITA to load with most media- have used both spoges cut to fit and floss. I rinse and reuse the blue carts- often opened to get the dang carbon out- until they are falling apart.