The Tele Vue Bino Vue Stereo Binocular Viewer w/ 2x Corrector truly provides a quantum leap in your observing experiences, and though quite expensive it nonetheless brings you closer to the mythical "spacewalk" experience than any other accessory at any price.
Using both eyes to view through a telescope achieves the odd duality of being both relaxing and thrilling. It is relaxing to not have to squint or cover one of your eyes, affording longer sessions without fatigue. And the perception of depth you'll get from using both of your eyes is an awesome thrill that you'll not understand until you experience it.
Though the stereoscopic effect of using two eyes shouldn't be relevant at stellar distances, in actuality that theory is plainly dispelled. The background sky seems cast far beyond the star, an inky black canvas setting off the object of interest like never before. Subtle nuances of double stars are revealed for the first time despite dozens of previous gazes. Though less than half of the previous amount of light reaches each eye, it nonetheless seems brighter because your mind's eye "gains" much more than is lost by the prisms.
Unlike other 45° binocular attachments, Tele Vue's Bino Vue sets up as easily as installing an eyepiece and does not require focusing adjustments if you have to change the interpupillary distance.