I'm currently setting up Upsource for the Netty project at: https://source.netty.io/
We had a few issues here and there, but it seems like most of them are sorted out.
The biggest problem was that Upsource does not let us choose the version of Maven for the build/analysis. Because Netty requires the newer version of Maven than what's been shipped with Upsource, the indexer failed to index correctly. (i.e. index was unavailable for most commits)
To work around the issue, we replaced the Maven in upsource/lib/upsource/tools/maven with the latest version of Maven (3.3.3).
It would have been much nicer if there's a way for a user to specify the version of Maven when creating a project (or editing a project.)
Also, even after we updated Maven to the latest version, we could not figure out how to tell Upsource to reindex the project from scratch, so we had to delete and create all project again, which was somewhat painful.
I really see the potential of this product, so I hope all the usability issues and customizability issues are sorted out as more releases are made.