Known in the trade as a Jaxa tool, this is fine to use if you know what you are doing, but in the wrong hands it can do untold damage to a watch. As someone who works in the industry I know this by seeing some watches come into my shop where customers have trashed them using this tool! The problem with this tool is that the watch needs to be clamped firmly in a solid base and you need to use the tool completely level and you have to apply firm downward force, otherwise you will slip and damage the case back. Also, you may be able to replace the battery cheaper than with a watchmaker but they have had years of training to test for circuit and movement faults during the battery change and also clean the watch, replace various gaskets and recheck water resistance. If you use your bare fingers to put in the new battery you will drain off so much power it is hardly worth doing the battery change and oils in your skin will corrode the metal parts inside and draw oil out of the jewel holes, thereby increasing the need for future expensive service work. This tool comes with four different fittings to fit many case backs, but you will only use one or two sets regularly and although it is easy to adjust, it also becomes stiff very quickly and you will need to regularly oil and maintain the tool. One of these I had completely fell apart after only a few months use! Most watchmakers don't use this tool as they know how impractical it is and they use a more expensive, but stable, watch opening tool. But then they do it professionally and need the correct equipment! For home changing on inexpensive watches that aren`t worth taking anywhere professional, and using the other right tools, this will do the job. Just makes sure you also purchase finger cots to cover your fingers, or buy plastic tweezers; and if you go anywhere near water (even washing hands!) then go to a qualified watchmaker, it will save you money in the long run!

Feel free to check out my blog which can be found on my profile page.