The module calculates slope and aspect values for roads, using the DEM. The tool is designed to work with roads in forestry and open-data DEM. You should not use it on roads with engineering ...
My gut feeling was that the slope map based on OsmAnds DTM underestimated the steepness of the terrain (which would not be good for avalanche risk assessment), so I compared it with Sonnys 50m DTM and ...