The v1 and the v2 are the exact same form factor. What the Tuffwing kit doesn’t allow for is the L1/L2 helical antenna. I made my own mounting but am not seeing any great increase in accuracy with the M2 vs the M+ in the air. I also had an add-on board which powered the M2 and wrote the events instead of the light sensor but looking back on it I wouldn’t go through all the trouble again.
This is because you used GCP’s. It always reports 0 because the value is in meters and you GCP tagging is probably within an inch which is 0.025m so the rounding doesn’t catch it. Look at the RMSE of the camera locations and the GCP’s inside the report.