I use machines like these sometimes for indoor work like warehouses & Shopping centres.
Used a ride on scrubber for an underground carpark where the ceiling was really low.
They cant really clean oil patches etc.
Theyre ok for removing builders dirt & dust, but You need to sweep rubble up before running them over floors.
The squeegees get clogged with small objects sometimes, and you have to stop to clear them regular or dont get an even clean.
Like you say, they cant do stairways.
Theyre ok to use in certain conditions, or to do a large area, & finish off with a pressure washer around stairs/walls/pillars etc.
Outside work, i would rather use a pressure washer.
Tim.