I have a 10 gallon tank that I switched from an Aquaclear HOB to a foam filter, and my 20 gal. quarantine tank has always run one. I keep a large one as a backup incase of a motor failure on one of the HOBs on my larger tanks.
Positives:
1. Less current in the small tank.
2. Easy to clean.
3. Easy to place.
4. In my opinion are about par with HOB in regards to distraction from the fish, ie appearance. Black and unobtrusive.
5. Because the current is slow around the intake I can plant right up to the filter.
6. Really good with fish fry.
Negatives:
1. Doesn't seem to have as much filtering power, just a feeling.
2. My wife doesn't like the sound of air pumps, have tried many but none meet her specifications, I wish Little Giant still made the Silent Giant airpumps. This is a big negative in our house hold. I can sleep with industrial noise around the home but the 60hz buzz of the pumps drives a lot of people mad. One could run a line and have the pump in a different portion of the house but that doesn't work with all tank locations. As the pumps get older the seem to get louder.
3. A few times I have had the hose come off the connectors. I do have check valves in place but have had the check valves come off too. This is likely due to cheap clear silicone tubing I am using. A HOB can break and drain water on the floor but that seems to occur less than a air line coming off and starting a siphon. It has happened to me a couple of times during setup, and one person from my office had to replace their living room flooring because of a siphon in an air hose drained a few gallons overnight.
Overall they are a low cost alternative to the HOBs and with care and attention are quite functional for a lot of applications. I wouldn't use them for tanks that generate a high bioload.
