You're probably looking at this product because you just received a watch that needs links inserted or removed.  Go to the jewelers or do it yourself?

This little tool is far from a masterpiece of machining or industrial design.  It simply uses a screw arrangement to give you a mechanical advantage so you can push a pin out of the link.  As long as you're very careful lining up your work, it will do fine.  If you don't line it up, you'll snap a few of the pushers.  The tool comes with several pushers--enough to do a couple of watches.  In the end, you'll be happy you saved a few bucks.