One is Elektron based so 1 MIDI port is required and the other one is Akai Force based so it can use both MIDI or USB class compliant. Using USB frees up the Force's MIDI port.
On the Midronome the USB port is not linked to any particular port but reacts to play and stop messages whatever the MIDI 1 or MIDI 2 is sending it.
I'd be happy to
1 - link it to one or another or, and that would be the best
2 - to command it separately via the tap tempo button.
This way we could connect 3 separate devices, being able to stop, change project or whatever, and get back in sync. Or at least in case of the 1st option have a real separate clock for USB class compliant devices.