Hi skyflash,
It has never been our intention to make licensing or contract work difficult. Quite the opposite: we wanted to make the license agreement as liberal as we could.
For most applications you´re allowed to use and re-distribute Tobii´s intellectual property for free. But if your application is a niche application (that is: expensive for end users) then we ask that you get in touch with us so that we can discuss licensing terms.
Considering the example that you gave, if the company that you wrote the app for charge $100 to end users, then the niche application rules don´t apply. The company is re-distributing Tobii´s intellectual property to end users as part of their app, and so the normal licensing terms apply. No license fee.
What about the contract work then? Well, it´s the price charged to the end users that should determine if it´s a niche application or not, regardless of what the company paid you to develop the software. I´ll see what we can do to make the licensing terms more clear on this point.