I wouldn't ship a loosely maintained open-source kernel driver to paying customers. You can get CBFS for less if you're an indie shop, but the don't directly publish the price anymore. Compared to spending a year writing a gross Windows filesystem driver or hiring somebody to do it CBFS is amazingly inexpensive.
I looked at it some years ago, but couldn't justify the cost for what I needed a FUSE like ability for. And moved on to a couple of other things.