I did this recently. It's nice to have entirely sandboxed Google services, and I like the dot that shows up when there's sensor access. Storage/Contact scopes are fantastic. There are a couple of cons though, such as not having Call Screen, and no form of any charge limiting / charging control for battery life.
It's a good experience and I can recommend it whole heartedly. Use an external way of controlling the charging to protect the battery, GrapheneOS' developers aren't well informed when it comes to battery management.