The best advise a friend gave me when looking at BRTFS stability was to look at the mailing list, and see how many puppies it was killing.
While it may be the default for boot disks, boot disks are rarely multidisk raid.
There are a number of shortcomings with RAID5 style configuration (Write holes, poor re-balancing, etc) which made me feel decidedly uncomfortable trusting it with my data.
Which is a shame, as from a convenience point of view, being able to simply add disks of varying sizes would have been much more convenient.
I went with ZFS in the end. (Only about 4 months ago, so the info is reasonably current)