NavList:

Re your question, my opinion is as follows. Astra 3B. In all honesty, I'm a backyard navigator, that in quotes. I have used one of the above mentioned, standing on the beach in North Carolina taking sun shots, also sun and moon shots when both are visible during the day.  Planet and moon shots at night too. My calculated positions are usually within a couple miles of GPS coordinates. Using an artificial horizon at home, my calculated positions are usually closer than that. By the way, I understand that the New York Merchant Marine Academy used Astra sextants. Price thereof might be a factor  but my understanding is that the Astra 3B is a quality instrument. In conclusion, there is a lot of junk originating in China. There are also quality items. Good shooting.