Nice! When we chose a time tracker for consulting, having a paid option that is also open source would have been a major pro point (so we can rely on it not disappearing, and being able to fix blocking issues ourselves).

You mentioned here that you don't want to add tiered pricing, but I do recommend to add support for paying for a whole organisation in batch (N users, so that the individuals at an org don't have to manage billing separately and an admin take care of it -- the individual's time to manage billing costs much more than the monthly price).