Been painting and gaming for many a year and in all that time I've never primed my figures, although I do undercoat them using acrylic paint first. I've never had any consequences from not doing so, maybe you can get away with it on metal mini's especially if they've had two or three coats of varnish.
That said priming is something carried out by most, and maybe I'd be wise to be doing it also. So maybe my New Year's resolution should be to prime my figures!
I'm not a fan of using spray cans for anything if brush on is an option. I live in a part of the world were the conditions are often not good for going outside to spray, frequently windy and wet. I do own an airbrush but the clean up after is a bit of a pain so I'd still root for a brush on option. So the question is what is the best brush on primer? If tried Vallejo but was disappointed to find that it was peeling of the figures!
Many thanks in advance.