Is it safe to update it to 4.0.4?
Give it a couple of weeks or so. If you are a regular user or depend upon your wallet to constantly pay and receive money a bug on the wallet can be a piss-off factor. But very less likely that there would be such a bug in an alpha release. You can read the changelog as posted and see if the new features are useful to you and if you really need them immediately.
With time though it is a wiser decision to update it when you can.