The black finish is a standard anodizing, but it’s been bead blasted. The hardcoat is a different way of anodizing. It’s a thicker and harder coating.
I have both of them, I think they both grind equally as well. Hardcoat “can” eat strings, but it depends on how it’s finished. I think the biggest one that got that reputation was the AntiYo Bapezilla 2. I personally think it had more to do with the blast that was done to those than the finish, but it was an easy fix. Just rub the catch zone on a leather belt or denim and it smoothed it, or like I did just play it and it smoothed out. I haven’t had any issues with my hardcoat Kuntosh eating strings.
The Kuntosh is an amazing yoyo, hope you can find one!