All my bikes are bi-cycles so I regularly get two tired.
That said, half my bikes are fix gears. Yes, real upper body and arm training if you go uphill. (But different from these hand cranks. The fix gear isn't aerobic for those arms but yes, repeated isometrics for real. Also core.)
Got the reminder a month ago at Cycle Oregon. I'm an old man so no, I didn't ride those hills (well, not most of them) in my 42-17 but instead flipped the wheel/swapped cogs to 36-21 or 24, but still, it was no sit and spin session. Afterwards, tired muscles and minor pulls throughout my body.