Something I noticed when using this is that partial parries resulted in my taking 0% physical damage. I tested this with a non-reinforced grass crest shield while fighting Champion Gundyr. If I messed up the parry timing and got a partial parry, I'd still lose all the stamina I normally would, but I wouldn't take the partial damage. As such, it was less risky going for parries because I wouldn't get hurt from a partial parry.
I haven't tested this very extensively though, so it could depend on the particular shield, damage types, or enemy strength. I'm also if this effect of damage blocking on partial parries is intentional or not. I also didn't test this with the regular version of the spell to see if that one had some kind of similar effect.