Buy cheap, have a nuked tank with thousands of $$ in livestock dead...
Worse still Seffie, cheap heater cracks spilling electricity and molten copper in your tank, killing most inverts and corals quickly, and fish shortly after that. Not even time to overheat or loose temp...
My reccomendation: get mid-range heaters and replace them every 2-3 years. You can sell the used ones if you like. Compared to the value of livestock in the tank, an extra ~$25 every 3 years should be valuable insurance...