This $9 watch is the simplest and most utilitarian timepiece I have ever worn. It is easy to read, has an adequate (not blinding) illumination, is small, light and comfortable but also tough, and has a battery that will last up to 8 years (with many other reviewers noting that it lasts even longer).
The F91W is a distillation of a digital watch. It has three features: tells date and time, has an alarm clock, and works as a stop watch (only up to an hour before it turns over). The functions are easy to use, and aren’t distracting.
I originally purchased this watch to use while running, but found that I liked it so much that I now wear it all the time. It has replaced my larger, more expensive Citizen Eco-Drive which is now reserved for dressier occasions. After swimming and showering while wearing the watch I trust its “water resistance” and am impressed with its durability. Its also cheap enough that I don’t worry about it breaking or getting stolen.
If you are looking for a simple, capable digital watch that will last for years, this is the one to get.