i wouldnt consider it as a serious proposition to replace a dedicated GPS unit but for the sake of £20 for the app and £20 for the chart (which you can also view and print from in a very powerful desktop copy of the application) it's a great little extra to have on your phone, either to play with on the ground or just to check your position from time to time in the air. for example i will shortly be doing my QXC using charts and dead reckoning but i like the idea of having this little app in my pocket just in case.