When I received the watch, neither the heart rate nor backlight functions would work due to a nearly dead battery in the watch. This is no doubt the result of this watch being very old stock, since this model has been out of production for many years. Replacing the watch battery cost $5 and about half an hour of fiddling with spring pins and microscopic screws, then countless resets to get it working properly. Ill give it 3 stars for basic functionality, but really don't appreciate the initial hassle, and many customers would simply return it as being defective.

Update on 6/30/2018 - The watch is working fine, however, the English section of the instruction booklet has a dozen blank pages. Fortunately, I am also fluent in Spanish, and that section of the booklet is complete. Otherwise, it would be really difficult to figure out how to use and setup this watch, which is very convoluted and not at all intuitive.