The Celestron stereo binocular viewer permits the user to view solar system objects (planets, the moon, the sun) and some deep sky objects using two eyes.
While not truly stereo, binoviewers produce remarkable 3D-like views. Using two eyes is more natural, and more comfortable with less fatigue. The added bonus of using two eyes is the roughly 30% improvement in what you see over using one eye.
If a Barlow is required to reach focus with your telescope, you will experience some increase in magnification (roughly 3x using a 2x shorty Barlow).
If you have a Sky-Watcher collapsible Dobsonian, you can shorten the telescope by about 5" in order to reach focus without using a Barlow, with the only negative side-effect being a small reduction in effective telescope aperture. The most recent production of these telescopes features a second set of detents on the poles to help you fix the length for use with binoviewers.
Binoviewers require two eyepieces with the same focal length, field stop, and similar focal point (parfocal is best). Don't forget to pick up a pair when ordering this product.