As far as the second part of your question of wether it's worth buying, that's will depend completely on your needs.
Third part of the question? How many years does it support? Not sure what you're really asking here. It'll continue to work as long as you have a MotoZ to connect it to. On that front, the Z3 series that just released appears to be the end of the line for the Moto Mods. Once that happens, you'll either need to carry around two phones if you need to upgrade for any reason, or spend the money on a dedicated camera.