Yeah my knee doesn't appreciate the impact running at the moment, working on getting that sorted out and repaired! Hopefully I can do it but we shall see hehe. I enjoyed the arc for the impact-free running.
The craziest thing I did on the Arc was trying to do the Pikes Peak course. It was just all crazy uphill stuff lol I couldn't handle it and only did like 20 minutes.
Good luck with the knees!