Earlier this spring I sold a
Kramer VP-790 to a local university venue for that very use and it has worked out quite well for them. Their knowledge of video formats is very limited, but they haven't had a problem getting an image from whatever source shows up.
The on-board test pattern generator comes in very handy for those last minute arrivals, too. The venue personnel can go ahead and get things in place (aligning the screen that lives on a fly system, etc.) and confirm operation of their part of the system so that when the guest speaker finally shows up they can look like they know what they are doing.
The front panel "hold to reset" button that returns the output to default configuration isn't a bad idea either.