We cannot know exactly what happens after we activate a tech so its really gamble sometimes. They should have "Activate","Deactivate" feature so we can choose which tech we can use. For example, I just activated Challenge 4 and I wish I did not. Because I was reaching 2m hardly and now its 4m but chests are not doubled. I want to deactivate it but ofcourse its not possible, yet.
Its not problem,if you just can get 2m then let it be,but if you can get 4m,more kill chest you can get and more item you can get too from killing chest