For those who are interested, I've contacted DJI about using the iPad 4 and their initial respond was not recommended saying that the telemetry information etc. may not be correct. When I explained that all I was trying to do is a test flight without relying on the app information i.e. I would only rely on the app for visual and limit my flying to under 10 mins. to be safe. They then confirmed that it would be fine and that flight control via remote is not in anyway controlled by the tablet/app which is all I wanted to confirm. So I did take a less than 10 minute test flight and everything (telemetry and video) seem to work perfect even though I did not attempt to use the RTH or auto launch feature via the app. Since this first flight earlier this morning I've picked up an iPad
Mini 2 and all is good. Bottom line is it seems that an iPad 4 works but is not recommended and this could well be due to the tablet holder but DJI did not elaborate.