The market display is good even if only for the ease of taking screenshots (press power + home) of price lists, on the iPad you can see quite a bit in one screenful. I wish they recognised that this is what people will be doing anyhow and allow saving previously known prices yourself (preferably in game as well as in the app).
Otherwise the app is quite pointless, and the animated background probably eats up quite a bit of battery. Also, it required me to sign in again when I opened the app today after first signing in yesterday - I hope this will not be a regular chore.
However, I see great potential in enhancing the game UI with such an app: add the system and galaxy map with route planner to the app, and suddenly you don't have to break spaceflight while you're plotting the course. And touch-screen gestures would make the map very navigable.