In sump? or in tank? I just ordered mine from autotopoff.com $50 for dual float in sump switch. And I will just get a 900 utility pump since I have to pump out of a brute garbage pail (40 inches head)
a dual float is to protect from the bottom float getting stuck in the on position, if the water hits the second float then the pump will turn off. You want dual floats.. The one from autotopoff.com is pretty nice. I got the bend your own version so that I know that it will fit on my tank.... Any pump will work with it, it is just the float and controller that will activate the pump.