In the website its written
"One license will be valid per application on a single operating system. The above prices are per each license."
1. if I have to build Android App only then I have to buy one license.
2. I can use this license only for one application.
3. I can upgrade my app as many times as I can and will not be charged additionally.
4. I will get free upgrades if there is any.
5. I can distribute my app to "n" no of clients with no additional cost.