BTW... the bio-viewer is pretty darn good on Jupiter, Saturn, Venus, and the Moon! Looking at DSO in them is not any better than a single eyepiece, and a bit dimmer. It's comfortable since you don't have to squint one eye. The views could be described as "3 dimensional", to some degree.
I'm using it on my Dobsonian reflector, so I had to put a barlow on the front of the bino in order to reach in-focus. Without the barlow lens, I could not run the focuser in far enough to reach focus. The up-side of that is that the views in the bino, with the 13mm eyepieces in it, and a barlow lens, are comparable to using a 6mm eyepiece!! Nothing like looking at planets and the moon with some hefty power.
I usually bring them to the sidewalk events, and they get used when all we can see is the moon...