You may have noticed that your device will respring into safe mode whenever the public version of Activator is installed on iOS 8.4. The problem is, many tweaks rely on Activator as a prerequisite, and Activator hasn't been updated to work with iOS 8.4 as of yet.
Does that mean that any tweak that relies on Activator is simply unusable until Ryan Petrich pushes out a public update? Not at all. Just install the Activator beta...