Alarm, backlight, stopwatch, 8-10 years battery life. 20-30USD price tag. What is not to love?
Terrible UX. Cycling through the modes steps you through the settings mode. A destructive / disruptive function should never be part of the normal functional flow.
I recently got an A158W (the shiny version of an F91W) because I want to drop a Sensor Watch board into it. I'm going to make damn sure to modify this aspect of the firmware.