I do work for a guy who uses the Dema block solenoids. They're a pain in the ass. They get stuck open for no apparent reason, and when you open them to clear debris that's never there the seat falls out (along with the two o-rings) if you aren't hyper careful. If pressure gets trapped, you can't just loosen the stem and relieve the pressure or the o-ring comes out of the seat and gets pinched and cut when you tighten it down. Also when there's a pressure issue and the solenoids can't open, the coils get so hot they melt themselves to the stem.
Otherwise, they're great.