We have to accept that the primary form on geolocation today is a GPS or similar (Galileo, loran, etc).
Thus a sextant in most cases would act as a backup. The cheapo plastic sextants (even cheaper that the ones you you mention) have an accuracy of about a mile or two. For what I know from salty guys, the most expensive sextant and accurate watch (with an experienced operator) give you about 1/10th of mile of accuracy. One mile is good for high seas, and you could use more accurate piloting techniques close to land.

I'd think that a plastic sextant will do as a backup for the GPS. Unless you are the kind of guy that like to be represented by possessions. If so, nothing says "cool mariner" like a good bronze sextant in an old wooden box.