i have a 2.5 gallon myself and i tried that heater out. i liked the look and it looked like it could heat my tank well. i brought it home from petsmart, followed the directions and plugged it in.
after 30 minutes, it didn't turn on. i unplugged it, waited another 30 minutes, then plugged it in again: nothing. i left it plugged in overnight and in the morning still nothing. maybe mine was just a faulty one, so i just returned it. i've heard others around here have it and say it works just fine.
but i've also heard this one works really well: http://www.amazon.com/gp/aw/d/B00106...5154673&sr=8-1
i plan to buy that one soon.