..Then, my mate bought one for his car as the blower stopped working...in winter! he said it was a pile of poo basically, drained the battery big time and barely heated a dinner plate size of screen.
Mind you that may be all you need on the boat. But anything that turns electric into heat will cane a battery. Theres plenty of tales with things like vinegar wiped over a screen stops the mist...but the facts are... condensation forms when theres a greater difference between inside and outside temperatures. So more heat inside...means more condensation!
Praps just leaving a side canopy open can remedy this at no cost!