I own a HHKB[1] and while very pleasant to type with the fact that the function keys are on another layer can be cumbersome in some IDEs. In IntelliJ IDEs you have Ctrl + F9 to build (or something like that) which means pressing Ctrl + Fn + 9. Maybe the experience can be improved with better placement of the Fn-key (which on the HHKB is in the lower right corner).
Reading the comments about experiences with split and/or ergonomic keyboards makes me want to try some other variants.
As a Vimmer, the HHKB is very close to perfection. I can reach every key without having to move my hands too far, the Fn key fall right under my right little finger and Control being in the correct place is a huge win. The fact that it has Topre switches is the icing on the cake, I wouldn't use any other keyboard on a prolonged basis.
Reading the comments about experiences with split and/or ergonomic keyboards makes me want to try some other variants.
[1] https://www.hhkeyboard.com/