All possible screenshots would be nice.
One time price for most sofware will have an initial payment ($100 for example) which include let's say 6 month or 1 year of support, when support period expires the client will have to pay for renewal (say $50/yr) to get support or download updates.
It works best for both sides, it keeps the developer motivated to release updates and bug fixes and keep the customer happy which usually results in more business for the developer, on the other hand with subscription the developer don't have to do as much.
If a major security flaw was discovered in the module, customers with active support will be able to download the update, customers without active support will have to renew to get the update.