There is a good reason for the delay in releasing it to public beta testers (or for that matter not releasing it at all to them).
Lets say the build is a disaster and ruins your mac. Developers are probably better at fixing it than the general public. So it makes sense to give it to them first - just in case it is a disaster.
True, but public beta testers are suppose to know what they are getting into before proceeding. Apple makes is VERY clear to backup, and that they are not responsible.