If you're sold on these bins, by all means buy them.

Your original post talks about "supurb colors." I don't personally think that color fidelity or even chromatic aberration are all that important in astro, where most of what you're seeing has very little color. What does matter is sharpness and brightness. So I'd look for bins with low levels of coma, astigmatism, field curvature, and transmission. An entry-level roof usually won't do well in those areas. See the Allbinos review I posted a few levels up.

For birding, I care about on-axis sharpness and don't care much about edge-of-field sharpness because for handheld birding you typically center whatever you're interested in. For astro, where you use a tripod more, edge sharpness matters more. As stars move across the FOV, it's a pain to keep re-centering the tripod. A large "sweet spot" is a blessing in that situation. No bin will be perfectly sharp all the way to the edge, but some high-end models come close.