I want to add (because I learned that the hard way) that you should always transform your “bool” variable with the bool filter in the playbook. If one day you decide to use AWX/AAP, your variable will always be a string even if you thought you send a bool.
So the correct way to write your line:
when: use_handler is true
is:
when: use_handler | bool is true
Or even better (and supported since Ansible 2.10):
when: use_handler is truthy(convert_bool=True)
From the documentation: Tests — Ansible Documentation