Lots of good discussion in this topic. I use straight through 10x50s with an Oberwerk monopod, and either stand or sit in a zero gravity recliner chair. I have found that I can go from horizon to zenith with this range of options.
But when you are observing the zenith, it's physically impossible for the monopod to make contact with the ground. It still has some value in terms of inertial damping, but that's not as good as true stabilization.
Personally, I like astronomical instruments to work either straight-through or with a 90-degree viewing angle.
A straight-through erect image, as in conventional binoculars, allows me to switch naturally and effortlessly between the naked-eye view and the optically aided view. The penalty is that I pretty much need to be lying down, or at least reclining, to view objects that are high in the sky. And that requires either hand-holding the instrument (not feasible much above 15X or 20X) or a large and complex mount.
A 90-degree viewing angle totally gives up on the correspondence between the aided view and the naked-eye view, but provides maximum comfort. I suspect the reason this option is so rare in the world of binoculars is that there are some serious optical penalties associated with erect-image, 90-degree prisms. And very few commercial manufacturers are willing to provide the mirror-reversed views that come from simple star diagonals.
Homemade binoculars and binoscopes, by contrast, tend to provide 90-degree mirror-reversed views, in my experience.
As for the 45-degree viewing angle, it's a plausible compromise between astronomical and terrestrial viewing. But at some level, it provides neither the naturalness of the straight-through view nor the comfort of the 90-degree view.