As it says in the FAQ, the feature set of the free version is not intended for the production of professional games and interactive content. That means you need the Pro license.
Actually I have to contest you on that point.
It says that the 'feature set' isn't 'intended' for production of professional quality content. It doesn't say that you're not allowed to use it for such, it means that the feature set is scaled down (for student use, primarily) and will not provide everything you need for a AAA quality/budget title.
You're still allowed to make a game and sell it with the free version, but once you hit 100k USD you need to purchase the Pro license (it's also worthy to note that this is based on the fiscal years, so you could actually be in excess of far more than 100k when you truly legally need to purhcase the license).
It's the exact same kind of deal C2 has, only with different amounts. Considering most people are fine with the requirement to get a business license if you hit 5k USD with C2, the 100k limit for Unity Pro should be more than enough.