Major difference is most likely the resin and the bonding agent in it. Most claims of hardness is not relevant except for the fact that it does tell you of the concentration of siloxane in the actual resin that goes on your paint. I'm guessing Black Edition has a much denser concentration of SiO2 in the resin vs Pro edition. Pro edition is also most likely a single layer of resin with SiO2 and a bonding agent underneath while Black Edition has the layer of SiO2 resin but also has a more concentrated crosslinking agent mixed in with the SiO2 mixture along with a different siloxane component on top to slow down oxidation.