Are there any release notes for this release yet? I'm assuming this is a stable release and safe for us to apply now?
You can find the release notes for that service pack here:
Composer 4.3 SP4 Release Notes
4.3 SP4 has been available for a couple months now so should be stable. The latest composer release now available on the Australian shared Composer instance is 4.4.
I just realised 4.4 is available. I should read the info on the Composer home screen more often!
ETA: I cannot find the 4.4 release notes though?