With Ritteri that like to climb glass, I did not want to risk having one of them get stuck to a plastic strainer, with the sponge there is not so much suction place in one spot, so they are way les likely to get stuck, and if the do no damage will be done because nothing will get sucked in. They also work great for nutrient export, once a week I rinse them out, and all kinds of missed food, and general garbage come out.