I've used a lot of Stits Poly-Spray silver on real aircraft many years ago. It appears the Rand-O-Fill is simply a non-tautening Butyrate dope with silver as a UV protectant, same as the Poly-Spray silver. I have never used the Randolph silver, though. I assume that it is similar to the Poly-Spray in that it serves the same purpose. Might make a good basecoat for filling and smoothing minor imperfections before the colors. Or you could simply use it as a silver color. I also expect it is high solids and will add weight quickly.
But no personal experience with it, so I probably shouldn't have replied at all. But since I typed, it, it's as easy to hit "post" as it is to delete it.