Chris,
I've used/using the prefilter. For around $15. it' a good little investment. It works well for what it is designed to do, but can be a pain also. I always have to keep screwing around with the little spongy thing which is a pain to keep it set "just right". Then again, I am topping off manually. It fits nicely over the rios but seems a really tight fit over maxijets, but it is doable.
I don't know why, but they also seem to come in 2 different models. One is taller and thinner the other is shorter and fatter. Of course, I could have one prefilter and one bubble trap, and am to stupid to know the difference :lol: