Not to mention they are bulky and awfully fragile. The case to protect one is what makes in bulky. You can buy cheaper plastic ones but they are not very accurate. Mainly used for training. Not very accurate as the plastic is very temperature sensitive and they tend to warp.

In addition to a horizon, you will need maps with latitude and longitude on them. It is difficult just getting an accurate fix from the sextant. That is half the battle. The next issue is transposing your fix to the charts (maps). It is a time consuming process.

What is wrong with a good old fashioned GPS?