choose a type which according to them would improve heat transfer.
Lots of semi-technical, semi-correct, semi-misleading "information" exists on the web about coatings of all kinds, including ceramic. First, any black coating of any kind on a head will increase the emissivity and thus increase the heat loss to the air due to infrared radiation. The emissivity of black paint is ~5x better than bare Al, and even shoe polish would be better than bare Al. Unfortunately, there are two catches to this. First, the heat has to travel through the relatively low thermal conductivity paint to get to the top surface where it can be radiated away. The further the heat has to travel (i.e. the thicker the paint, and the lower the thermal conductivity of the paint), the greater the temperature drop across the paint, and thus the worse the heat transfer. Only in the sense that a high thermal conductivity black coating is "less worse" than a low thermal conductivity one could it be said to "improve" the heat transfer.
Second, thermal radiation is a relatively small part of the heat equation anyway. Convection carries away much more of the heat than thermal radiation, and
any coating on the head is worse than no coating. That is, even if the head could be coated with crystalline diamond (which has very high thermal conductivity), the heat transfer to the outer surface would be lower than if the head were left bare (albeit, in the case of diamond, only a tiny bit lower). Again, one coating could be said to "improve" heat transfer only if that statement were properly qualified to say it was iin comparison to the use of a worse coating, not in an absolute sense (e.g. "A head coated with silver improves heat transfer over that of a head coated with paint").
The above isn't directed at any specific company offering coatings. Whether or not such coatings had higher thermal conductivity than black paint only could be determined by examining the technical specifications of the material they used (both its thermal conductivity, and the thickness of the coating).