Although funny, it had problems actually rendering the correct font and there is also a huge bug as it made hubspot forms disappear on several sites.
I'm sure it's not malicious but it is a bug and as the add-on isn't being actively developed everybody should remove it (his twiiter account has been suspended any way so ...)

Giving it 2 because it works on Chrome (and it's great!) but not on Firefox. PLEASE make it work!

The font is unreadable. I don't like it. But nice try.