Thanks for the feedback. Actually, beta testing for SLB 2.0 has been going on for several months now. Development has reached the point where it is ready for release to the public. However, as WordPress is used in so many different ways, it is difficult to know whether a certain user's particular configuration will cause an issue with SLB. This is why SLB is released as a release candidate and is also the reason why I've added this message to the update notification.
Installing or updating any plugin can cause issues and testing plugins on a staging server prior to updating a staging server is always recommended. This is already common practice for most website owners, so the message was added simply as a friendly reminder.
Of course, all WordPress updates are and will always be optional. It's completely up to you whether you want to install the update or not. Notifications of betas and release candidates are made for the convenience of brave users who want to test the latest and greatest features that SLB has to offer. The feedback from these brave users is invaluable. If you don't want install a beta or release candidate, then just ignore the notification and sit tight while others test these versions to make sure it's ready to go for everyone.