I suspect they can be accurate enough if you can calibrate them against a known ‘proper’ spl meter; but if I had one of those I wouldn’t need an app!
This is rapidly turning into a rabbit hole. I was initially just curious about how ‘quiet’ my living room really is, and was surprised to find it somewhere around 40dB. I’ve just measured again (washing machine now finished two rooms away) and get ~35dB on my (Android, Sound Meter PRO) phone and 37dB 30 second average on my iPad (SoundMeter X)
What’s your experience?