I just see Grayjay as an imposter. It is less private and completely bans forking to start a new project.
Take a look at what is now the Fossify app suite. It was Simple mobile tools but that was bought out by some Israel firm. It was forked and is now Fossify mobile tools. The old Simple mobile tools is now not on F-droid.
If Grayjay turns into a scam there is no legal way you can fork it. You are completely locked in. That is my primary concern.