It’s not totally clear where the elevation data is sourced from but I imagine it’s the (near) global shuttle radar elevation data (since the app has an international reach). As such, this not brilliant, especially around high gradient features (ie cliffs).
A bit of a project but: much of GB has been “heighted” using LiDAR and subsequently had terrain (“the ground”) and surface (tops of trees and buildings) models created with 1 or 2m (planar) resolution. You can then use QGIS, etc. to create shade maps at very high resolution.
Of course, broadly speaking, it’s generally pretty obvious when -approximately- a given crag gets the sun…
