Is it really free?
- There are no license fees
- There are no hidden premium features you have to pay to get access to
- There is no pay wall
- There is no requirement to share your email address in order to download
- There are in practice no restrictions on neither output nor bundled graphical assets (all core asset such as the base mesh, targets and skins are shared under CC0)
The add-on as such is open source and can be downloaded from GitHub.
See also Can I sell models made with MPFB? and Can I use models made with MPFB in a closed-source game?