I just bouth 4 x 3 pack of the foam inserts for my two AC
20's to send in for rebate. I was going to order them online at AquariumGuys as they are the cheapest online. But I was at PetSmart today and they are clearing them for $1.97 per box of 3.
The carbon really helps with orders, I don't know why you say they are worthless. I will be getting those at AG's, since again they are the cheapest on the 3 pack of carbon.
I didn't know people use the sponge's longer than 2 months. I'll have to start doing that, just rinse them out in aquarium water during water changes. But even if they last for months for each one, Getting 12 sponges for $3.94 (after getting the free ones) comes out to 33 cents each. Too good to pass up.