I had a great experience with Zenyum! Many of these reviews seem to be from before having collecting their aligners, but I am writing this review as of almost completing the entire Zenyum journey. Had consistently good customer service with very prompt replies. The app is a little buggy at times, sometimes photos will glitch or messages may get lost, but ultimately the customer service helps to solve all problems with very little fuss. My teeth have definitely become noticeably straighter, and they are pretty much the teeth that I had hoped for before starting! It was incredibly convenient, because there's no need to go for regular monthly appointments. Checking in is all done through the app, and all the aligners are provided in one go.
Would definitely recommend Zenyum.