My opinion would be to just buy a solid working heater. Don't waste your money on that when all you need is a good single 250w heater that will work when needed. There are countless threads about heaters... lol everyone has their own opinion and which model is best, so just do research and see. I use Aqueon pro's and have been VERY pleased with this new product. Been using for over a year and a half now and not one issue. It holds the temperature I need it to, heats up the aquarium VERY fast, and is a solid product that won't break or leak (it's not made of plastic or glass)
The 250w is good up to 90g and I'm currently running one without any issues.
So save a ton of money by using only one good reliable heater.
Hope this helps!