We have the Pro license and we've been using it for quite some time now. There was a question made 8 years ago about Typescript definitions for the library, is it still in the queue?
Old question: https://forums.daypilot.org/question/3266/missing-typescript-definition-scheme-for-daypilot
We're in the process of fixing type issues in our project in order to have a more robust code base. It's a big codebase, and Daypilot is a crucial part of it. Having type definitions would be very valuable for us. We're a long time satisfied customer, and we'd really like to continue with Daypilot, but we might reconsider because of this refactoring, which makes type definitions mandatory going forward.