You can use that kind of paint — if I'm not mistaken, [USER=22220]@Grumpa[/USER] does all the time, for example. However, are you sure you'll be saving if you do? Sure, they're cheaper in money, but are they also cheaper in time if you have to keep mixing the colours you need? Or if you have to go over something four times instead of once or twice to get them to cover? Or if they clog your airbrush because they have much coarser pigment than modelling paints do?

Tamiya paint is noticeably cheaper if you buy it in 23 ml bottles, BTW. Paints you know you use a lot, you probably don't want to be buying in 10 ml at a time.