Nik,
I have been using some Vallejo Model Colors for about a year, my wife got me the Earth Tone pack for Christmas last year. I paint Battletech miniatures and I found that the went on very well with a brush. The squeeze bottle they come in is easy to use & prevents spills, but I found you really had to shake them a lot to make sure they were mixed. I also agree with what others have said about how easily the Vallejos would rub off. So it is important to dullcoat these to protect them.
I did spray them from my Badger 200 and they did pretty well once they were thinned. I more recently had my 200 refurbished by Badger (for free!) and I also bought a 100G. With the new brush, I ordered a set of Vallejo Air colors off eBay (25 colors for about 58 bucks). I used my 100G (fine) for the first time to base coat soem Mechwarrior DarkAge minis with the US Light Grey. I had already primed these with a can of white enamle primer. Unthinned, it sprayed very cleanly from the 100G though that's not the best brush for basecoating admittedly. My only problem was that the paint dried very slowly and in some places accumulated to the point where it almost ran. And in some cases, the thin paint did not cover some dark areas of the plastic very well. As I was alternating light coats on 5 minis, I was concerned about this happening all the time. It had been raining a lot that weekend, and I was in the garage so the humidity may have been a factor. I added some alcohol but that didn't seem to help much.
I tested out my refurbished 200 (fine tip) by putting another light coat of the US Light Grey on the same minis. This time it went on better and dried faster (I was in the basement). I can't say it dried fast but it was much better than my first attempt. I also spayed some of the their primer onto some microarmor tanks. That went on nicely and I rubbed my fingers over it later after it dried and it stayed on.
One nice thing about the Vallejo Air paint is that it has little if any volatiles in it. So when you spray it, you don't smell any appreciable fumes (at least I don't). I have used some of the Tamiya acrylic on some minis and it seemed to have a lot of fumes for an acrylic. It worked nice but it definitely had an odor. I also bought some of the Vallejo Air matter varnish but I haven't used it yet.
Has anyone using the Vallejo air noticed that it is a bit slow to dry? Does the Vallejo thinner help it dry faster, or slower?