How would you have structured it differently then? 

Remember, your bargaining position is somewhat weak due to having put enormous resources into developing something no one else has ever developed, so you likely would not be in a position to demand full payment up front, especially as there are final kinks to work out before production. But the tech works (the buyer has seen it), it's just a matter of making sure the production in volume will be perfect.

What other kind of deal would you have made in such circumstances?