Metallica IS using this in every single concert they have played after they experimented with them in the Antartica show. AxeFX II, but I saw AxeFX III in a recent photo.

https://www.youtube.com/watch?v=P6k2ghtbhoU 3:09-7:32.

Megadeth is also using AxeFX. https://www.youtube.com/watch?v=O7vzOjzn0Mw

And from there you can extrapolate how common they are.