you're right it's.... special. Let me give you my thought process:

  - One time pricing can be a real hurdle for users to pay upfront. Remember adobe costing a lot of money up front. The upside is that after this initial huge hurdle your free to use the product. For the business non recurring revenue means they need to batch changes to make buying the product worth while. This results in a long cycle between updates.

  - Subscription pricing aligns the business with it's users. Users pay only for what they use and the business can ship features to the user as fast as possible.

  - The downside is the subscription is often 'per user' and is done on an ongoing basis. You pay for the tool even if you don't use it.

  - Usage based pricing: you only pay for what you use in the smallest quantity that is understandable. This is what I use and what AWS uses for example. I think this is a really fair pricing model. If you're only doing one project it might cost you 3 bucks, but if you are a company that uses the tool fulltime you pay accordingly.

It might turn out that too many people are turned off by this pricing, I don't know. It is easier to change to a regular pricing model then to a weird one :-).

If you open one of the examples that is one project. Your project can be published at one unique URL.