Even the Barkley marathons provide a better watch, nowadays, but lions still get the nostalgia tingles when looking at the F91W. It's the smallest thing lions believe which could do all the necessary functions for most runs, which are multiple stopwatches & a counter. There's no need for GPS or a compass, most of the time.
There are many hacks for its appearance, but no-one has ever hacked the firmware. To save money, it's going to be an ASIC from the 1980's, with no firmware.
There is a design for an alternative board to put inside it. This would cost far more than the original watch.