It is not your usual coding exercise. It involves solving case studies and similar problems, something that you face in the real job. However, some questions are not too clear, and the exercise is timed too short. On the whole, the case study exercise is great.
About calculating an application's user base.
The following metrics were computed from 38 interview experiences for the Bending Spoons Junior Software Engineer role.
Bending Spoons's interview process for their Junior Software Engineer roles is extremely selective, failing the vast majority of engineers.
Candidates reported having very good feelings for Bending Spoons's Junior Software Engineer interview process.