I have had a lot of experience with Aqua One heaters, I currently have 3 of them (all 150W) in 3 small tanks. I do not trust them in my larger tanks, as they were causing fluctuating temps.
2 of the 3 no longer work correctly. One is heating at 24 although it is set to 28, and the other is set to 24 but is heating at 32.
I had two of the Aqua One 150W heaters in my 300L tank. I then got a 150W Jager heater, and decided to test it out in the tank, so I swapped it out for the left heater. I noticed over the next week that the temperature became stable, so I tried removing the other 150W Aqua One heater.
That tank has remained stable since. One Jager 150W heater was more reliable than two Aqua One 150W heaters.
I have just bought a 300W Jager for my 500L. I wont ever buy Aqua One heaters again.