well, all these rubbers, Xiom C55 & O7CG, Donic Bluegrip C2, Donic BlueStar A1, Dignics9c, have one similar point - they come alive when you engage the sponge.
I played the most with C2 (albeit on my old all-wood blade and shortly on the current TMXi) and C55 (with current blade, TMXi).
C55...