It's hard to tell.
The polarised lenses in my sunglasses make it almost impossible to view the compass bearings, and the central display is dark unless I switch the dash lights on.... which dims the display...then my co-driver gently reminds me to stop becoming distracted
We were pottering around the D'Aguilar NP along the Mt Mee forest drive last Wed. There was a lot of overhead tree canopy, slow driving (<20kmh) because the road was very rough. However on the odd occasion I glanced at the compass on tight turns it appeared to be moving freely.
I'm not sure whether the gps for the display map is coming from my phone or the Gren. It seems to work OK with the phone in my pocket and wireless connection using an OttocastAir2 pro for Android auto.
I would very much like to be able to illuminate the compass all the time so as to be able to read it under all ambient lighting conditions.