Rejex is some interesting stuff. We use it on all 8 of our aircraft with stellar results.
In particular, it keeps the exhaust from staining the paint.
I did a test with Rejex when I first discovered it. I was thinking that it was another so-so product. So I coated a taped off section of the heli tail right in the exhaust stain area.
I then treated the other squares with my favorite and some other products I had.
Rejex worked, the others did not. Simple as that.
We still have NO exhaust stains on the helicopter! The Pilatus remains easy to clean and the Extra 300's always look good.
As for cars, it is OK on paint, gives a fair shine and lasts a few months. But it works wonders on my diesel rear bumper!
Chris