Depending on which company it is I wouldn't over complicate the matter. Stick with however the manufacturer specifies it so if they research it (it's possible) they get the same answer.
Here's how I answered mine a few months back:
GPS Navigation: GPS/GLONASS
Visual positioning System (VPS) for low altitude stability
Vertical: +/- 0.1 m (when Vision Positioning is active) or +/- 0.5 m
Horizontal: +/- 1.5 m
(The above is for DJI Phantom 3 Pro)