https://www.boonex.com/forums/topic/Trident-is-now-UNA-Update-9b2-released-.htm
The software is MIT-licensed. Pricing plans are for support, hosting, customisation and access to automatic updates (and support) or some modules (Premium Apps). While in Beta, all apps are free.
If you "buy" an app once, it's yours forever, only one-off or one-month payment is enough to use it indefinitely, also under MIT license. If, however, you want to access direct technical support for the app, you need to purchase a monthly subscription for this app. Otherwise, you won't be able to download updates via Studio.