Just found this old post and thought I would give feedback on my experience on those robust switches.
I've installed two waterwitch 230 in 24v on my 80 ft wooden boat sometimes in early 2014. Ship's been leaking quite a lot in the early days and I've tryed many mechanical switches before to keep her afloat. Those waterwitch are expensive but don't have any moving parts
that can break. The first years the pump
were switched on every 5 minutes in average (big leaks
, small money), today it's more about once every 2-3 hours. Never had any issues with those two switches, still work
like a charm. They need a clean up sometimes when the bilge
is too dirty since some dirt tent to accumulate behind the metal plates keeping the switch ON longer than needed (just throw a bucket of water on the switch or use compressed air).