I'm Android developer having the best on the planet handheld Star Chart app in my portfolio (DSO Planner - it's not exactly the planetarium app, more like a professional tool, but still having similar capabilities). You can trust me on that:

1. The smart phone compass (and the inclinometer as well) is just slightly more precise compared to a primitive button compass. Moreover, its data is unstable (put it on the table note the azimuth and orientation, grab it, put back into the exact same orientation - most likely you will see a different azimuth value). Any real compass would work much better (and not consume the battery).

2. If you have a knowledge of your location with even a 100 miles error, your planetarium software will have an error in objects positions of just 1-2 degrees max (the Moon may have an additional 1 deg. error in a worst case due to the parallax effect), which is comparable or below the accuracy of your ordinary compass measurements. Besides, you have a topo map at hands to orient, right? (they usually have the coordinates grid or center's coordinates imprinted)

Even though you have a GPS on your phone, it wouldn't tell you the direction, unless you are moving fast enough or/and record and periodically monitor your trail path on the digital map. Don't be fooled with the car navigation apps, they are approximating your position and direction using the map data (aligning the GPS data with the road lines exactly).