Casting directors rarely, if ever, need a self tape in 1080p let alone 4k. The file sizes end up being huge and a pain to work with. Slatable compresses the imported video to 540 x 960 and optimizes the final video file for web delivery.
If you have been asked to send in a 1080p or 4k tape do! Always follow casting director instructions to the T.
If you want to use the iOS camera and import your Takes into Slatable shoot in 720p. If you shoot in 4k or 1080p video Slatable will compress the video which takes a bit more time with larger resolutions. So shooting in 720p will not only save you device memory but also a lot of time!