Do you mean three-button navigation?
If so, you can change by going to Settings > Gestures > System navigation
Another factor is water ingress.
[Edit] - See also the list of USB-to-jack digital to analogue converters.
Also linked to your third point, lack of FM radio hardware, since as Urs pointed out, headset wires have traditionally been used as the antenna. Personally I would have liked FM radio to be available but I accept that the FP4 is already too big and heavy as it is, and that FM radio is going to be low on priority lists for several reasons. There was a lot of discussion back in the day, I think all the points must have been made …
But if you want to use an old FP2 as a FM radio why not, that would be greenish, if you don’t mind not changing the battery … Oh dear!