Have you considered the Black Magic Pocket Camera 4k/6K? I know it is bigger in size but it comes with 5 inch monitor and once you add the monitor to the Z cam, size becomes similar. But with Z cam you’ve got an extra housing/monitor to deal with.
In terms of the maturity of the whole system, I will personally choose the BMPCC over Z cam:
12 bit color depth,
BRAW is integrated in Davinci Resolve,
BM color science,
You get Davinci Resolve Studio (Noise reduction, great stabilization - available in the free version of Davinci- needed for both cameras)
1 extra stop of Dynamic range cording to https://www.cinema5d.com/z-cam-zraw-vs-blackmagic-raw-which-one-is-better-our-lab-test/ useful for shooting big structure, schools of fish, in ambient lightwhere light and where artificial lights can not be used.
All required video monitoring tools are available such histogram, focus and focus peaking etc...
Autofocus (Push focus, not continuous focus) useful
https://youtu.be/uZvRvOoL-88
https://youtu.be/qkL1S5kuS-Q