i've used an elite stingray 5 for a smallish betta tank, and two elite stingray 15s for a 20 gallon and a 12 gallon tank. they worked really good, but unfortunately i had to replace the one in the 12 gallon with an elite hush 20 because the current was a bit too strong.
later on i got an aquaclear power filter for the 20 gallon, but the stingrays did a great job!
the guys at my lfs told me that for the price you cant really do better...
summary: i would recommend it (purely out of personal experience)
Excellant filters! Have a 5 for my betta tank - the current is a tad too strong but it's multi-directional (360) so I can fiddle to send it backwards.
Also, they come with little carbon/zeolite containers which, if you are careful, can be opened, emptied and re-filled with normal media balls or something to convert it into a biological filter from chemical. They are extra easy to clean and really do the job.