We do something similar at our startup. Basically we're a communication tool for construction, maintenance work and visitor management. Our selling point is simply data consistency, e.g. you can't edit posts, unlike on Facebook, and deleting will give a notice. Photos taken from the app are signed and location stamped. I think it's interesting that people comment you can just take a photo of an odometer, but that's not something that two parties do all the time; it's best to just automate that process.

Blockchain is not a "killer" feature of the app, but it's another layer of security. Databases are the core, but staff with access can edit a database in seconds. Maybe one way to think of it is like cash registers. The person operating a cash register can still steal it, but it's a lot harder than if it were just a box. It won't stop a dedicated person, but will greatly discourage doing it casually.