Pre-thinned paints

I never heard of modelflex products. However, I don't know of any prethinned paints out there in enamels or acrylics. Alclad is AB ready but that's only for NM finishes.

I use Model Masters acrylics and they are as thin as I have seen. Some colors are thinner than others but I still have to thin regardless. It's the nature of the beast as far as paint goes.

Andy 

Personally I don't think it's a good idea to use "airbrush" paint like createx, air-tex or modelflex for modeling - they are rather garish colors than can be hard to mix to the correct shade, don't take weathering well, and generally are intended more for people who will be playing with their airbrush on paper or cloth. Stick to Tamiya and MM acrylics and Gunze lacquers for modeling.