Yes, it can be a bit messy if care isn't taken, but with practice, the only mess might be on your fingers - but it washes off very easily !
SNJ products used to supply metallic paints, and the polishing powder, which I used to use 25+ years ago, but they are no longer in business. The powder used to cost around £3 or £4 for a very small jar back then, so when I confirmed it was very similar to jeweler's polishing powder, and the same stuff as the finger print powder, I found a UK supplier, and bought two tubs, each twice the size of one SNJ jar, for about £2 each !
I apply it to the bare plastic first, then spray on ordinary silver paints, and, when dry, apply more powder and polish - very simple.
Here's what the tubs look like, alongside a SNJ jar, and an example of polished finish on my as yet uncompleted F-104a.