Mutually exclusive follow ups help you activate one branch at a time. These follow ups can only be created in "opens" or "click" criteria, here is how you can do it:
First you create a template with the criteria 'opens' and condition 'yes'
Then, you create another template with the criteria 'opens' and condition 'no'
This way you can confirm that only one of each branches will be sent to the recipient. You can also check: How to create mutually exclusive follow ups?