I don't have F91. I used to and it been with me in some life changing experiences.
I do have F105 an F158. Not my pic.
F105 was around since late 2012 and strap is broke (no warning whatsoever). It's been good watch and frankly if i find strap for 5-7$ i will replace it.
If not, i will grab another F105. I like these. Some people do it too
Casio F-105 watch. Classic in form and function.
Over the time Casio produced several models with same functionality but different design.
I can name W-87h
Which is officially cheapest Casio in Canada but i saw chines knock off one time in thrift store. F91 is not alone in that.
The other one i can recall is
and F10-1A which probably thinest digital Casio watch as today.
Some people here rock W217
So who else uses simple F91 like (functionally) watch and what you see as slim simple replacement?
So far for me it's either F91/105/158 or W217