Michael,
Putting them on the dash is not a big issue, routing the hot air hoses from the heater can be a challenge.
I've got them installed in my Cobra they look nice, and they are about as much use as my heater is.......in a topless car???....NOT!
With the wind whipping around the cock-pit, I don't think the heat ever actually touches the glass of the window!
I would put the nice looking chrome demisters slats in place, but in my estimation they are not worth the bother to actually hook them up. I never benefit from the demisters whatsoever.
Of course I just don't drive in the rain either, and when I do occasionally get caught in a shower, the towel over my lap works nice on the window too.
Kevin