Well the Ubuntu wiki page says: "Boot-Repair is a free software, licensed
under GNU-GPL."
You can also take a look at the launchpad of yannubuntu (the developer):
https://launchpad.net/~yannubuntu
It says in his description that he is "dev of 4 GPLv3 apps: Boot-Repair,
Boot-Info, OS-Uninstaller, Clean-Ubiquity" and then you can also browse the
code there, you'll find this file:
https://bazaar.launchpad.net/~yannubuntu/boot-repair/github/view/head:/debian/copyright
So yes, Boot Repair is free software. I mostly just look for the source code
and then open readme, copyright or license files.