If one is not there, no difference in display quality can be observed. But outside the protection reflects unfortunately very strong. Even at the highest brightness, the image only very dull and you see instead himself, the sky or the environment. Very annoying. Especially for people who shoot mainly with old manual lenses this is a very big limitation, because these are very dependent on the display in order to provide focus manually. I do not know if I'm happy with such a restriction on duration.
The term "screen protectors" is therefore justified. Managed the display is very good, but unfortunately, before good readability outdoors. Degree in cameras without a viewfinder (only a few expensive models NEX-family have a viewfinder), it is not very helpful, to restrict even the display so.
Perhaps a protective film with its own anti-reflective layer would be more appropriate?
Note: photographers who work exclusively with autofocus lenses, can strike here in my opinion anyway, as you can see still enough and is not so dependent on the display, as is the case with manual focusing.