I have severe allocation issues in btrfs with recent kernels and
recent btrfs-tools when using thousands of snapshots. All the
community had to offer was "well, try to restrict yourself to at most
a few hundred snapshots".
btrfs rebalance brings the whole system to a halt until it has
finished, since it places some kind of lock on the file system. The
effect on the system's other seervice is severe up to "sit back and
wait until system becomes responsive again".
That's not what I'd call production ready. It's simply just betafs at
the moment.