thebullmoosesociety

Here are two comparison videos with side-by-side evaluations on a number of areas, like low light, slow motion, audio, rolling shutter, and how they key.
Part 1:
Part 2:
 
In short:
Ursa Mini: better overall picture (flatter shooting profile, better color gamut) global shutter, better for green screening
Nx1: sharper, less noise in low light, better audio, better slow motion