Although I don't currently use Upnote I did look into it at one point and found that they address the concern of how the app will be supported given the lifetime purchase option. You can check out their thoughts at https://getupnote.com/support.html. I can appreciate that they are upfront about it and are committed to honoring their lifetime purchasers. I will say that with some other software that I purchased through a one time payment that switched to a subscription model they did freeze the features, which is a more gentle nudge for existing users to convert to a subscription.