I purchased a visualiser for our school and have found it to be an invaluable resource for teaching. It is basically a modern version of the old overhead projector.
All you need is to plug it into a power socket and into a digital projector. It projects anything placed under the camera onto the screen, books, student work, models and 3D objects. You can take screen shots, record video and split the screen for a variety of purposes. It is a great way to share student work, share a story, observe a student editing their work, project a lesson on a hand held device and many, many more applications.