Why only mild? Because Domino's pizza is still made in a kitchen full of flour that's why. As such it is not recommended for people who suffer from celiac disease.
The new crust is made of water, rice starch, rice flour, potato starch, and olive oil.
To help you figure out whether or not, Domino's Gluten-Free Crust is okay for you to eat, they put together a video:
If you rather have something to read, they posted a FAQ (Frequently Asked Questions) regarding their new crust on their website here.
Domino's new Gluten-Free Crust is available in a small, 10-inch size only with prices varying by store.