Only once did I have a giant snail pull down both switches at once. I still use the same system today, and am just careful not to allow big snails access to the floats! Every now and then it is a good idea to spin them to make sure they are not gunked up with anything. They are pretty reliable, though I have had 2 go bad in about 10 years of using them.
And Grandis, I am still running AquaC skimmers! Old habits die hard. I've never been into expensive overdriven skimming when most of what they pull out is calcium carbonate
I think they are mainly just fancy aerators.