NavList:

I have a Troughton and Simms pocket sextant which I purchased on e-bay about 15 years ago,and on my opinion it is excellent. I used it many times both on a boat and on land, and I can rely onits altitudes with 1' accuracy (this is the limit with which the scale can be read reliably). I am not sure in what yearit was made, possibly in 19 century. And it was not expensive (I don't remember exactly but certainly less than $200, but this was 15 years ago, and I do not see them frequently on e-bay). 

In many e-bay listings, it is difficult to tell a replica from a genuine one, and most of the listings are replicas. One needs very good pictures, especially of the scale. I can send you pictures if you wish.