According to Mel Seder:
I'm assuming the "bleeding" in this case refers to the humourous euphemism "bleeding edge", which would certainly suggest that its not ready for prime time.
Actually, I wouldn't put either of the above xcyb repositories in the default yum.conf if you're running automatic yum updates via cron. I'd put them in an alternative configuration file, and just specify that manually when you want to get something from the xcyb repositories. For example...
yum -c /etc/yum-xcyb.conf update
Of course, you won't get automatic updates for any packages at those repositories, but they're not likely to be critical anyway. For some sites that provide alternative versions of packages that are part of the base distribution, it might be safer to not have the "updated" automatically.