i brought the torque app and the Elm 327 Bluetooth plug in 2 weeks ago for the exact same reason... to check my boost.
its ok, fairly accurate but not as good as a direct plug in using Vag Com.
my boost spiked around 12 psi which I think is about right, all in all cost me around £8 for the app and mini Elm 327.
you can also read fault codes if your engine management light comes on, it does all sorts just have to play around with it.