Lots of good exercises. Nothing that will really expand stretch your musical imagination, per se, but great for getting the feel of typical flatpicking licks & embellishments into your fingers.
All the song examples in the second half are true bluegrass/country/old-time standards. I knew the author was an authentic flatpicker when he listed 25 standards that “you almost certainly know already” and I didn’t recognize one + no single rendition of any had more than a few thousand listens on Spotify.