Check this out:
I have one in my 3g Betta tank and two in my 12g Killisfish tank - only been one week - I will add a flollow-up review once I have used them longer:
I like that these are flat heating elements - I had a molly once, Spartacus, who died by wedging himself between the heater the tank wall - it was awful! I never want to see a fish burned by a glass tube heater again! This fits flush agaisnt whatever surface you put it against so no fish can get stuck!
Also, during a water change, if the heater is not turned off, the glass can shetter! Let's not even think about that one! This heater functions safely in or out of water (althoug it is intended for underwater use and it is not recommended to operate in dry environments -it will be perfectly safe for the amount time it takes to do a WC). Also, low heat output means it is safe for aquarium animals and plants.
And, not nearly as important, but aesthetically, this is a nicer option - it can even be placed on the floor under the gravel! For bare-bottom tanks, it can be placed anywhere you might be able to camo. it - like behind some plants! And, it is perfect for people with black backgrounds (like me)!
The price is great! For this prive, if the heat is not enough, I can just add another one! Besides, it is actually hard to find the right heater for small tanks - most are for minimum 10g tanks - so this gives some nice alternatives - like Betta tanks!
The only drawback is that the heat is not adjustable - you have to keep an eye on your thermometer and plug-in or unplug as needed - that said, look at the price!
I am very pleased with these so far! Anyone ever used them?!