in the exact same way i use my 60%'s or a touchkeyboard on the phone where everything isnt available at the top layer.
via function layers as easily used as shift or alt gr after a short learning time, we're humans, and our ability to adapt and put stuff in our muscle memory is pretty awesome! (i guess playing guitar for a large part of my life helps with that though.)
i got a Gon Mobik and while the layout is a little bit enhanced versus the JD40 everything comes down to one thing, the ability to map the keyboard for stuff you actually use and remember that, i'm quite surprised at how easily i adapt to using the mobik even though i don't even have "åäö" thats used alot when i write in swedish in my first layer :)