Material Usage Flags Cost?

Curious if anyone has looked into the cost of material usage flags? I’ve got a master material used on a ton of staticmeshes and want to use this same material on a skeletalmesh.

I’m wondering what would be best:
A - Leave the staticmesh material alone & duplicate the material for the rarely used skeletalmesh version
B - Add the usage flag

My understanding is the usage flag is adding statically defined HLSL code, so the cost should be insignificant or non-existent to the staticmesh version. Is that correct?

Only cost is that then material instances will have more permuations. So more shader memory usage and more compile time.