This is good. Having an alternative to Pixel-Phones for GOS makes sense. I wonder if we will have the option to buy a Motorola phone with GOS out of the box (not sure if i would trust that, but it might be interesting for some people that are skeptical of installing it on their Pixel by themselves).
This is a good step for users wanting more options for GOS. Pre-installed choices could address worries about installation for those who aren't comfortable doing it themselves.
Same owner (Google/Alphabet): https://blog.google/company-news/inside-google/company-annou...
AFAIK you can verify the integrity of an existing GrapheneOS installation.