Actually they do if you go to a paper that the refer in a link http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1121/1.4865269.It would be helpful, if they had direct links to the apps in the article. There are at least ten different apps in the Play Store called SoundMeter.
I just got me a calibrated miniDSP UMIK1 for about 130€. To me makes a lot more sense than wasting money on shady PlayStore content.
For most people who just want a general idea of sound levels he apps work fine.
Don’t see what’s “shady” about them