I have used it on my Audi. I'm not sure if it is overly accurate. Then again, I don't know what my car is boosting at to compare it with! There is a lot of faffing about in the Torque app settings to get it somewhere near ready for testing.
It goes up to 18psi on my app. Not correct for a 2.5 derv I wouldn't have thought?!
I have it working on mine, but also have nothing to compare, tested it in my mates octavia VRS and it was giving same readings as his boost gauge, the horsepower bit was interesting. But all other readings were alright too. It's hard to configure on first setup so the wiki definitely is useful
I'll second what jimmcgee said, I did this once, but lesson learnt. The torque app itself isn't bad at all, some of the features are a bit pointless (like the 'eco tree') but it's fairly decent. When I was down Santa Pod a few months ago the quarter mile times the app showed were not exactly the official times but close