totally agree for a shrimp tank they are amazing filters. shrimp make very little waste and the amount of grazing space for the shrimp is huge.
the only real downside of these is the look. I dont run one on my fissidens tank because its so beautiful to look at, but I do have a small shrimp breeding tank with a HMF powered by small return pump. basically its like those little prefilter sponges on and intake, but about 100Xs bigger and no need to clean it.
Thanks for the links bostoneric, I've read a ton of info on this before I decided to try it. In realty, fitration is filtration, no matter if it's a big sponge like thing, a sump, 9 canisters chained together, whatever as long as the BB have a place to grow. The advantage I see with these and shrimp tanks is these allow a huge sponge for shrimp to graze biofilm from, one of these favorite things to eat and should be their main source of food. Needs very little maintenance, etc. When looking to go with a 16-20 tank shrimp rack, I don't want 20 filters I have to clean weekly,
I've seen a lot of people too drill a bulkhead behind the sponge wall for water changes. Open the ball valve, drain the water out to the desired level, close the valve and add new water, all without ever risking sucking up any shrimp or fry because the bulkhead is behind the mat.