The license seems ambiguous though because there's no LICENSE file in the repo and the website has copy about requiring a paid license to use the software; the only place GPLv3 is mentioned is in the README. I opened an issue requesting clarification.
Edit: no idea what the software mentioned above does, just correcting a common misconception.
If I'm incorrectly co-opting some open source nomenclature, I'd love if someone could let me know. As I said in the issue linked above, I do need to update the purchase website to bring that language more inline with what's on GitHub.
It's perfectly legit. You can find the sources for these items elsewhere on the web but the hassle and security implications just aren't worth it.