Jerry,
I purchased the EMS-HW50C and installed it myself in a couple of hours three years ago. It works great when plugging into shore power I can check the display and know immediately if there is a problem or if everything is good to go.
So far it has not allowed power to the coach because of low voltage and a bad ground. Low voltage seems to happen more often than it should.
A friend of mind just had to have almost all his on-board equipment replaced because of power surge; one of the AC's, a Microwave, DVD Receiver, the TV and the Fireplace controls. It happen up near Fort Bragg staying at a RV park.
It really gave me piece of mind, one less thing to worry about.
Regards,
Bill