I wouldn't use software like that. Imagine you build a company using some software, and it was free until you hit $X in revenue. One day far down the road, your company is doing well and you start to get close to $X. You realize you have to acquire a license, ask them for one, and now... you just have to pay whatever they ask for? You're locked in to someone who could quote you whatever price they want. Unless it's really easy to rip out this software, it seems like a huge pain.