I ordered this one :http://www.petsmart.com/product/inde...=Aquarium+Size which is in the mail coming to me bc NO stores sell it locally. People here seem to like it but many other feel the ones that are not adjustable can be a nuisance! This small betta therm one only heats the water a couple degrees above room temperature so you'll need a thermometr and a stable room temp!
Seems like there are bad reviews on that one, let us know how it works out! I use the tetra ones in my tanks, no issues so far and the temp is always at 78F.
I had one of those [b]ZOO MED bowl heaters, meant for 1-3 gallons. I put it in my 1 gallon, with Flirt, under rocks and all. and she dang near got boiled. Went into shock, but I saved her. she ended up with temp swb out of the deal. but she's 100% now, and happy. I just wanted to warn about them.
A heaters ability to maintain a good temp is also dependant on the temp of the room the tank is in. If you have a room that stays relatively warm than a lower watt heater would probably manage to keep up. However if the room gets cold, it might only bring the temp up a few degrees and then break before its time due to having to work to hard.