This isn't working at all like I expected. I am the host and I tested this with McTwist who was not admin at the time on my server.
I placed a baseplate. We both could build and edit our own bricks. He could not do anything with my bricks, not even build (or hammer) on them. I could only hammer his bricks, nothing else.
He placed a baseplate. The same thing. It appears that the person who placed the baseplate can do anything with his own bricks and also hammer other's bricks. But others can't do anything with that person's bricks.
I expected it to be fully public baseplate where anyone could build on, paint, wrench or break anyone's bricks. To prevent griefing there should be prefs to enable/disable these (build, paint, wrench, paint) features.
This add-on does not do that. I am disappointed.