I might be in the minority here, but I have been very disappointed in my Elos unit. I have had it for two years, and have replaced the pump twice, and the sensor "eye" once. If I manually try to activate the pump, I just get this weird little "burp" of water and the then the pump sort of twists and turns off.
I have a Tunze on my QT tank that I plan to eventually use to replace the Elos, and am very happy with it. Maybe I just got a bad one, but since I have basically replaced almost every component, one piece at a time, you'd think I would have worked out any issues with it by now?