I don't know about accuracy, but I do know that the app was very useful on my long drive last fall (9000 mile by myself). I am useless at taking notes and the Pocket Light Meter allowed me to take a meter reading (always matched up with my other meters, by the way), snap a quick shot of the scene and later have all the information I needed for the negative file. I was often shooting a Speed Graphic and I had boxes of negatives once I got home. Now I can look at a single photograph and go to the file on my computer that has a location stamp and exposure info recorded for that scene.
Many of us like shooting with "outdated" equipment, often utilizing our own sense of the scene, avoiding extra technological screens that can distract as much as aid us, whether they are alkali-battery operated, selenium cell or smart phone. Let's not become so technophobic as to miss an opportunity when one presents itself, even if it's on an iPhone.