I have used these a lot for the Betta tanks.It's enough filter to where it helps keep the tank clean,doesn't take up much space as you can hide it in the corner,and it flows slow enough to where the Bettas don't seem to mind the water movement.

Pros: Great for small Tanks

Cons: none

I used these in my smaller tanks. They are very durable, work well and cost efficient when you have several smaller tanks that need filtration systems.

Pros: easily changed, and cost effective

Cons: none

I find it works great in fry tanks if the airline tubing is attached to a valve to control the flow.Easy to hide with plants

Pros: great filtration

Cons: none

Penn-Plax World Replacement Filtration Units are very good. They are easy to replace.

Pros: doesnt cost very much

Cons: NONE

These are good filters, clean small tank well, but tended to fill up a little too fast.

Pros: easy to change

Cons: needs changing a little too often