I've a pair of binoviewer and I truely love it. Viewing with two eyes is an excellent experience, it's especially for brighter targets like the Sun, the Moon and the planets. Floaters in your eyes will be averaged out, color saturation improves tremendeously, sometimes you got a false 3D impression and the targets actually appeared larger than with single eye.
The only downside is, the image will be much dimmer. It will not be half dimmer after your brain merge the two splitted image, but it's really dim and that's probably explain why the experience is particularly impressively only for brighter targest.
Problem is, existing binoviewers are based on beamsplitter, that said, light will be divided into two halves and that's why it's dimmer.
Suddenly, I imagine if we could have ways to preserve image brightness when we do binoviewing? Here're two possibilities:
1. By use of a mirror: mirror can create a copy of a view without dimming the original view, wonder if that could be applied to create one more copy of our eyepiece view and feed it into another eye?
2. Electronic way: by using a CCD to pick up the image, and to use two LCD screens to feed the same image to both eyes.
I guess (1) may not be possible, otherwise, it should already be an existing product?
(2) is definitely possible, and image intensifying technologies can be used as well, to make the final image even brighter than the original. So, if any one is going to make a product based on (2), please tell me. :-)