If you want the best use MYLAR (2 mil thickness).its called matt paint where I come from
In that case, there is no problem mixing and matching reflective surfaces.Whilst I don't doubt that mylar is the best product if used correctly as it is the most reflective of the choices I am not sure that it is worth the extra expense.
But in any case, i'm not asking whether I should use mylar OR paint, what I want to know is are there problems such as hotspots or anything else with mixing the coverings used within one grow space.