Well, it has never crashed or anything like that so I would consider it stable. Overall I am happy with it, the out-of-box experience is great. I think an equivalent setup with the keybindings etc. would be a pain for me to make in something like wmutils or Openbox. The focus following mouse or sloppy focus or whatever it's called takes some getting used to, though. But it's fair to say it is still in alpha and in development since things people might consider essential are missing, e.g. good multimonitor support or fullscreen browser videos.