Looks like a very expensive stud/pipe/cable locator to me. I've had mine for around 20 years and it still works fine. Cost around a tenner, IIRC. A posh one now might set you back double that.
I think the screen is just a mad gimmick that will give people a false sense of security, as there are things that no detector will find, like plastic plumbing. I thought ahead when fitting ours, and stuck strips of alloy tape down everywhere there is a run of plastic pipe, just so they show up when using a detector.