My Church just acquired an Atem 2 Production Switcher and I am in charge of operations. The product functions quite well except for the fact that (1)I can't playback videos on it, we really need to be able to playback videos on it (2) There is a delay and an out of sync picture with respect to audio and realtime.
ATEM switchers do not have built-in video playback. They have two 'clip players' which can play up to 360 total frames, and are mostly meant to use as stingers and/or 'Bugs'.
The ATEM should only have a few frames of delay, but it also depends on what formats you are coming from and going to. Doing Up / Down conversion results in a fairly sizable delay, and for best results you should set your equipment to work in the native resolution of whatever your output device (projector, monitors, etc) is set to.