I have them, and they are rather on the small side, but bit larger than the plastic heads.
I will use them for Void Viridians who are rather pin-headed
my guess would be that they should be in the average range for any historical miniatures, and even for chunkier bodies they would simply change the proportions to "true scale", whereas making 25 mm figures more "fantasy style"
I was wondering if anyone yet has used them for what they were meant, replacing plastic heads??