Metered the same ten scenes with a phone app (Lightme), a Sekonic L-308 and the meter in my OM-2, then compared against what actually printed best. Results: the app and the Sekonic agreed within a third of a stop on eight of ten scenes. The two misses were both strong backlight, where the app’s averaging fell apart. Conclusion: the free app is genuinely fine until the light gets difficult.
Matches my experience — incident metering is what you’re really paying the Sekonic for. In flat Welsh hill light the app is fine; shooting into a bright sky, being able to walk over and meter the light falling on the subject wins every time.
For negative film I’ve honestly stopped metering half the time. Sunny 16 plus "Wales adjustment" (open two stops, it’s always duller than you think) has yet to lose me a frame of HP5.