Unfortunately, Air Display's name is now a misnomer as it would seem to indicate that it allows connection only over WiFi; as such, I was not initially aware that it also allows connection over USB. So I found Duet and thought it would do what I need. Uh, no: it caused a "hitch" in my mouse (which could only be resolved be a reboot: even quitting using Duet without rebooting wouldn't fix it), it was an abject disaster when used with mirroring (even if the iOS device wasn't one of the displays mirroring), and their support has sent me no response now for over 3.5 business days (other than the initial autoresponder).
Fortunately, I did eventually find Air Display and it's brilliant: no lag (on USB; I haven't tried WiFi), no hitch in my mouse, no problems with mirroring or with using as an extended desktop. Buy this now!
Show less