This is a low cost item and while it couldn't be described as a high precision tool, it is incredibly good value for the price (I paid $9.30) and does the job of removing screw type watch backs.  The tool also comes with 6 sets of jaws and a nice neat plastic case.  The tool is quite sturdy and solidly constructed .  I used some WD40 on the adjusting threads to make it a little smoother to adjust and it's now fine.  Unfortunately the spare interchangeable jaws aren't held in tightly within their slots inside the case and tend to fall out into the case, but that's a small negative.  The tool might not be able to work with very large watches, but is likely to be ok for most.  The jaws open to about 32 mm space in between each of the the three jaws when the small round basic jaws are fitted.  Overall this is a little beauty for the price.