Yes, you can use TakeLessons tools or manage existing students offline. You are welcome to add your existing students directly to your TakeLessons roster if you'd like to use TakeLessons tools to have your full teaching schedule listed in one place. However, the TakeLessons billing and payment services are only available to students who book lessons directly through the TakeLessons website. That means you would be responsible for collecting payment directly from your Reverb students. Of course, if you want hassle-free TakeLessons billing and scheduling for your Reverb students, they are welcome to go through the TakeLessons website to purchase lessons with you on. the platform. Bear in mind that the TakeLessons lesson price would likely be slightly higher than what you were paying through Reverb Lessons.
In order for you to continue charging your existing students your Reverb Lessons price, you would need to collect payments from those students directly (not through TakeLessons). That said, TakeLessons has lots of teachers who manage both private (non-TakeLessons) and TakeLessons students this way through their accounts – the tools are simple to use and the benefit of having your full teaching schedule in one place is well worth it.