There are good arguments for btrfs, and good arguments against it. One of the latter is that it requires you to think differently about your disk space, as seen here:
I'm all for new features. But things are a little different when you have a whole concept that you've worked with over decades turned on it's head, and forcing that concept on every user's machines.
Yeah I agree. Furthermore there are still some major issues. So I do understand that some people are critical of it. But under the condition that the major issues have been fixed by the release of omv 6, I do have a positive feeling about that.