That's fascinating, I just did some reading on this - I had not known that the basic technique of "mewing" is very similar if not identical to something that's been practiced in yoga for thousands of years. That in itself doesn't speak to its effectiveness necessarily but on the surface it's a different way to look at it than as just a modern fad.

Regardless, it doesn't cost anything to try, seems no danger in it and it seems logical that it could help.