The variety of rowing, treads and weight training. It's def a full body workout and works all areas of the body you are trying to improve. The coaches and staff are friendly too and it's not competitive. I also like the heart rate monitor.
I really enjoyed the personalized attention from Coach Vanessa. She ensured I kept my form throughout the workout and really pushed myself. I also liked being able to track my heart rate and splat points on the monitor. Outstanding experience. Highly recommend OTF.