Turns Your iOS Device into Another Display

I bought a display extender app that connected over WiFi. It was totally unreliable anywhere there was much radio interference, such as coffee shops or conferences. The hard wired connection make Duet much more reliable.

It still does not handle the display size and resolution difference between the two displays as gracefully as one might wish.

Its an excellent value for when you want to use two windows at once.

BobW1981 about Duet Display