NPG is great stuff for a race car, but I don't consider it practical for a street car. It can't be mixed with any water, so your entire cooling system, including engine, must be completely evacuated of water.
Also, what happens when you blow a radiator hose out in the middle of nowhere? Billy Bob's Pork Rind Emporium and Auto Parts ain't gonna have any NPG.
Also, we stopped using Water Wetter a few years ago after discovering Royal Purple Super Coolant Additive. In our street and race cars, we could see an 8-10 degree decrease on a real coolant temperature gauge, whereas we saw virtually nothing with Water Wetter. Royal Purple additive really works! (And of course, I carry it in stock...)