I've got six of these heaters, and every one has worked well, no problems.
I got the first one back in the very beginning when I didn't know any better, and it always worked well, so I just stuck with the brand. Two of mine have been running for over a year with no issues, so I can vouch for them for at least that long. The only one I've ever managed to kill was one I took out of the tank and forgot it was still plugged in. That one burned out...but I don't believe that can be blamed on the heater. :)
I hope that helps!! Also, if you get the heater at walmart, use it for a bit, and if it stops working, you can always take it back. They've got a very lax return policy, and will take it back even if it's been a few months if you tell them it stopped working. :)