This seems great, bit different than traditional audio tours. Especially for those who want to quickly explore the city, but don't know any locals, who could guide them.

In Paris, we went for a traditional guided tour ("Paris with Chris / City Free Tour"), which was great, but you have to adjust to their schedule and walking pace.

I don't see myself using this app together with my friends (as in part of the video), because we couldn't discuss the sights at the same time. But when I'm travelling alone, this seems like a fun option.

My friends in Prague running very similar service with standalone devices for almost 3 years. http://www.electronictourguide.com/

They asserts that it's impossible to make a decent guide in the format of the application due to limited resources of content transport, battery and disk space + risks associated with content protection.

What do your friends say about content protection? It seems like the least important thing to worry about since it's so hard to protect your content no matter what the medium.

Looks interesting. I wonder who does the narration. How fast will it roll out to other cities?

You can hear audio previews of all the detours here: https://www.detour.com/detours