I have an Aerobonus pilot figure. Older online resources seem to say that you absolutely must prime resin before painting. Newer resources say that so long as you wash it well, no primer is needed.
Who is right?
I’m using Vallejo acrylics for the color. I would prime in a black Mr. Color lacquer but would like to avoid it if possible since I have nowhere to spray smelly paints.
Personally I would prime the resin. Especially when using Vallejo paints as they tend to come off easily during handling if the surface is not primed.
I think with using Vallejo a primer is a must as it doesn’t adhere as well as other paints and could come off. You could use Vallejo or any other brand of primer. Tamiya has some nice rattle can primer that are prefect for a quick spray w/o the typical airbrush clean up afterwards.
Maybe I’ll do that. I have a rattle can of Tamiya lacquer grey from a previous project.
Some paints require primer also on styrene …
Definitely seems like Vallejo is one of those, even in my brief experience. But it’s otherwise a good paint and pretty much all my LHS stocks so I’m stuck with it.
I still do
I always prime my builds - it gives some grip for the paint, and turns it all the same base shade to avoid raw colours showing through. And with Vallejo I always prime plastic figs - it just rubs off too easily!
I have seen folks use different colors.
My current thoughts are black and then highlights with white or grey.
I was soooo gonna’ be lazy and skip the primer step today, but after you got into my head I cranked-up the spray booth and primed! 
—mike
I really like Vallejo. But I find it absolutely needs a primer and I usually seal it after