one could say that the visors are a crude and low grade version of Lancelot's "Not For One's Own Glory". It may hide their face, but if you recognise their voices, their devices or movements you can easily guess who they are. SHirou might have designed toem to look cool, but it was Shamal who fixed up the distortion aspect while Shirou imagined the details of their barrier jacketsIt is mostly a way to prevent muggles from finding out who they are, this giving them more leeway to act in their capacity as wolkenritter wheneven it is needed. Shirou himself will not be able to summon his own barrier jacket because the master program is still inert, as the 666 pages have not been filled yet ( and we all know what happens when that's done). HE will stick to reinforcement for his own clothes, but will be able to use a few speels by the start of the HGW.
The summoning of Saber will be followed by Shirou shaking the BoD to see how many more servant are still stuck between the pages.......