Relaxed, almost 3D viewing: Ideal for planetary and lunar observing
A bino-viewer turns your telescope into binoculars. Instead of the usual (and rather unnatural) way of observing using only one eye, you can observe in a totally relaxed way instead of having to squint. This not only means that you will not tire as quickly, but also that you will experience a 3D effect in your lunar and planetary observing. And also, the image will appear brighter and larger on physiological grounds. Even experienced observers will discover new details on the Moon!
The image orientation is not changed by the bino-viewer. So if you, for example, use an Amici prism to obtain an upright and non-reversed lunar or planetary image, then this orientation will remain the same through the bino-viewer.
You will need two identical eyepieces of the same focal length to be able to use a bino-viewer. Each eyepiece can also be separately focused on the bino-viewer.
A bino-viewer has the advantage of being able to observe with both eyes. However, these instruments are mainly designed for observing brighter objects such as planets, the Moon and bright deep-sky objects.
Very faint objects should still be observed using just one eye. But bright objects do appear particularly fascinating in bino-viewers.