Behaviour Tree Blackboards: Unsure of decorator terminology

I have a Boolean Blackboard key which updates correctly within my Behaviour tree. When I’m trying to use a Blackboard decorator I only have the option for “Is Set” and “Is Not Set” when I would expect it to read “True” or “False”. When I use Float Blackboard keys I can use operators like “Greater than” or “Equal to”, but I don’t understand the functioning of the Boolean version so well. The Blueprint Node “Set Blackboard Value as Bool” definitely changes the blackboard value to true or false, but does it “UnSet” the blackboard value? I just want my Behaviour tree to abort one branch when the bool is true and to abort another when it’s false. Why does it have to be so unintuitive? Is there something I’m not getting about Setting Blackboard keys?