There are features of btrfs that are currently considered experimental/unsafe to use like their raid-5 implementation.
I personally use btrfs raid-1 setups and have survived actual device failures without data loss. However, I also perform regular backups so I'm not overly concerned about "eat my data" bugs in a filesystem either.
I was under the impression that the data eating RAID5/6 issues were patched "long ago", but due to the write hole issue, which isn't likely to get fixed anytime soon, which means your data is (probably) safe, except for whatever was being written during the "write hole", and your array may crash and become read-only.
The kernel wiki says the following :
RAID56
Some fixes went to 4.12, namely scrub and auto-repair
fixes. Feature marked as mostly OK for now.
Further fixes to raid56 related code are applied each
release. The write hole is the last missing part,
preliminary patches have been posted but needed to be
reworked. The parity not checksummed note has been
removed.
I personally use btrfs raid-1 setups and have survived actual device failures without data loss. However, I also perform regular backups so I'm not overly concerned about "eat my data" bugs in a filesystem either.