Correct, each time you activate after you cancel the subscription you will have to pay the activation fee. It is a one time fee in the sense that you will not have to pay for it again as long as you keep the subscription going.
If you already own the products, and also decide to get the subscription model to get the upgrades, you will be able to use the extensions still even after you cancel the subscription.
The subscription model was created so that there is a lower price to be able to try the products and use the products to see if they are the right tools for you. If you are not ready to purchase the suite, you can instead go for the subscription model until you decide if you want the product or not.
