Documentation is pretty much nonexistent. It looks like it could be interesting, but I can't even tell what sort of operations, data types, etc. are supported.
To clients, it looks exactly like a memcached server.
It may indeed look exactly like a memcached server, but that's not enough. A client that speaks the memcache protocol assuming that it's talking to a cache can make assumptions and cut corners which a client talking to a persistent store ought not, and users and implementors of clients that speak the protocol need to be aware of these issues.