That is also the impression we got when we tried Mattermost. It came as a big surprise because we are using a selfhosted Gitlab instance and Mattermost is supposed to have great integration with Gitlab but it really didn't work well. Maybe it is due to us having set up Gitlab within Docker, I don't know. In the end we got it working but it still didn't recognize a user from Gitlab. It really felt like they had some good start and ideas but then something changed and came to a halt.