And I don't recall thinning them much. I used a few drops of their own thinner. Like a lot of paints they do need to go over a primer or base coat. If you just spray it on bare plastic you might have problems.
This is one coat of Model Color OD sprayed over Poly Scale Earth. It was not so thin it ran under the tape mask either
I find for hand painting that Vallejo paints can take a couple of coats but i thin those out a bit. Now I really dislike Model Air.