Self cleaning glass is coated with something that feels a bit grainy to the touch. First problem is the grainy surface hold dirt in the 'pores' of the grain, only a tiny amount, but it never dries gleaming. As others have said, the coating is matt
Second problem is the danger of damaging the coating.
Self cleaning glass works best when it has a good drop angle, 30 degrees or more. Practically flat like a lot of conservatories and I think its worse than plain glass.