Hi there..
I use mostly MM paints also.. but I'm not sure what you mean by "regular thinner"?
here is some info from the Model Master Technical Reference Guide on their thinners.
"Description:
"Testors Enamel Thinners come in a variety of sizes with 2 different formulation: one for airbrushing and one for cleaning brushes, the airbrushing thinner is a stronger solvent and should be used as a paint thinner, airbrush cleaner only."
Airbrush thinners come in 1/2 pt can and 1 3/4 oz bottles in the testors brand and the Model master brand. I have used both Testors and MM brand airbrush thinners and they are both the same thing.
The brush cleaner come in 1 3/4 oz bottles and 1/4 oz bottles and is different from the airbrush thinners.. a bit milder as i've used it for washs and also a couple of times for thining paint for airbrushing filters onto a models' basecoat. I've never used it for airbrushing a basecoat as It doesn't seem to mix as well as the airbrush thinner.
Model Master also makes 1 oz Lacquer thinners for their clear coats but I don't think these can be used to thin enamals.
Helpful tip #1.. Model Master and Testors airbrush thinner works very well to thin mm and testors enamals but is fairly expensive. I use mine only to thin my paint.. to clean my airbrush I keep Low odor mineral spirits on hand.. which costs about $2 a quart at wal-mart, which is a great way to save money as you use more thinner for cleaning the ol airbrush than you do mixing in paint...