I am a big fan of the 1.75u FUNCTION key. Too few sets provide it. In addition, it is almost universal for 60% boards to have a 1.25u FN key on the bottom row. It seems odd to me to have a FUNCTION legend (for when people like me configure a board to have FN instead of Caps Lock), but then not have a matching legend for the bottom row. I realize you can't comfortably fit FUNCTION onto a 1.25u keycap, so FN is perfectly acceptable.
SP has been providing both the 1.75u FUNCTION and 1.25u FN keys as part of their dyesub SA keysets (like Ice Cap and Industrial), and I have been eternally grateful for that since all the keyboards that I use with my iPad(s) need both in order to have legend accuracy.