> Is srcset commonly used?

It is, to provide a couple of different image sizes so smaller screens/high DPI devices can load the best-sized image for their use.

This is the best article I know on the subject https://cloudfour.com/thinks/responsive-images-the-simple-wa...

I don't know about its popularity, but it works as advertised and my company had used it. What's more important is that it's a correct solution for the problem (unless old browser support is required).