The best thing is that you don't have to prepare the original partitions in any specific way, like with bcache. You just add new partion and say - this is a cache for volume /dev/.... and it works. I don't know about performance differences - haven't used bcache that much.
The versions in readme are slightly out of date. Maybe that's what facebook uses internally, but the driver seems to work perfectly with higher versions. I submitted some patches to update function signatures in 3.9, but that was only to get rid of compilation warnings - everything else still works.
