My comments won’t advance the discussion about eyepieces, but I wanted to pass along that not all sextants work the same. I have my father’s sextant.

It’s a US Navy Mark II from January 1946. The long piece, which does have to be screwed into the body to operate the sextant and removed for storage, does not invert the image. It’s more like a rifle scope that blocks out extraneous light and gives a good sharp image of whatever you’re looking at. No pieces with pin holes, too. Instead, there are two glass lenses that you can rotate down into the field of view and rotate them until the glass goes dark (much like polarized sunglasses). I’m pointing to them in the first picture. It allows you to darken them just enough to see what you need to see without excess glare. Again, I don’t expect this to make any difference to the discussion, but thought it useful to know some sextants, even older ones, were much different.