We have a first aid company (Zee Medical) that comes to the office and fills the first aid kits once a month. They sold us those "urgent care" kits that stop bleeding immediately. Thank goodness we haven't had to try them out. But the thought of them sold us and the package is small enough to put in an individual first aid kit. So, even without knowing if it works I'm adding one to my first aid kit.
I believe it will stop a large open wound from bleeding but not aterial bleeding.
The Boy Scouts said it best "Always Be Prepared".