No, you can setup a dongle with bluetooth. In a regular zmk setup with nice!nanos or whatever bluetooth MCU, the two halves communicate wirelessly over bluetooth, a central one that does all the calculating of what key presses to actually send, and a peripheral that just sends raw keystrokes to the central one. But with a dongle setup, you’d get a 3rd MCU that you plug into the computer that acts as a central board without any keys that has 2 peripheral boards it communicates with. Because you’ll keep that 3rd MCU plugged into the computer, it won’t need its own battery or even any components, it can just be a bare MCU. You could also make a case for it if you wanted:

https://www.youtube.com/watch?v=YwsutNf1WRA&t=721s

Or get a 3rd MCU to use as a dongle so that acts as the more power hungry central board. Even with tiny 110mAh batteries, that’ll give you 3 months of battery life with a pair of nice!nano2s.

Functional as in it technically works or that its comfortable and realistic to use?

Mx spacing is 19.05mmx19.05mm. Choc spacing is typically 18mmx17mm. And this is 16.5mmx16.5mm? Maybe its just your hands but those appear even smaller than that.