No, the built-in GPS is not great when use use the Mavic features that require GPS on the remote location, when I use the Garmin GLO the GPS location data is very accurate.
Example, when you view your location on Google maps with the standard Internal GPS data, the blue position has the shaded blue area around it to display possible errors, but when the Garmin GLO is connected this shaded area is not visible.
Also the follow me mode works very well, move two steps and the Mavic follows.
Be safe and happy landings.....