Interesting. I have this kit and my first thought for creating the multicoloured splinter camouflage scheme was to use strips of Washi tape, as I would for any Laftwaffe scheme. Then I thought that I might have a go at producing a paint mask set. The problem there is, as you say, the compound curvature of the fuselage which would take me a quite a lot of trial fitting and tweaking.
These masks though should be spot as GasPatch will be able to draw the camo on the 3D drawings for the actual model and then "unwrap" them to a flat image. So these should fit perfectly to the model, despite the relative stiffness of the material
I might even buy a set for myself, if they do fit accurately, so I'm interested in finding out?
Do the instructions even tell you which masks mask out which colour?