I compared a cheapie SPL meter from Amazon against a cheapie SPL meter on iPhone. They were both within a fraction of a dB.
The thread I posted about this can be found below. To it in proper context someone claimed that their iOS iPhone update broke their SPL Meter App. Not so. I proved it using my iPhone and SPL meter App vs the dedicated cheapie SPL meter from Amazon. While not totally scientific it was clear that the SPL meter and iPhone were both reading within a fraction of a dB of each other. The original poster claimed that the iPhone was 10's of dB off since the iOS update. Not so. Must have been operator error.
This $25 SPL METER from Amazon seems to do a fine job for me.
