My impression is H9 fixes airplanes as they release new models. They may improve the manufacturing process on older models (such as the Corsair and P-51) but if you want improved landing gear, etc. you should go with one of the new models (P-40 or P-47).

I think this is mainly due to the relatively limited runs they have for each model.

I've heard their 150 size P-47 has really benefited from their experiences with their other warbirds.