I am old school to the max. I have used Humbrol. Thinned down of course. Having said that Humbrol is out of business! Michaels sells an acrylic flat water based paint.
Humbrol is not out of business. Going quite strong though their paint doesn't brush quite like it used to.
You used to be able to get a great metal look from their silver. Not anymore.
I have a bunch of the acrylic craft paint I got for other projects and they are pretty versatile. They're replacing my dwindling stock of Polly scale.