I've found them easy to work with once you get into it.  I've learned a little goes along way, it's easy to overdo. It may look like you haven't done enough when they are still "dry", but after the pigment fixer is applied the colors really stand out after the fixer has dried.

You can scrub most of it off if not to your liking, and go back over it again. Multiple layers I think add to the overall weathering effect. I have mixed some pigments into paint to give it a gritty texture, like rust on exhaust systems or dirt, with good results.

Looking good GaryG64.