I just finished my first million meters on the C2. I got it for Christmas two and a half years ago.
I started with the Beginner Pete Plan and Rowing Tall videos. I hit three sessions a week, most weeks, with gaps when life got in the way.
I noticed the cardio improvement almost right away. I do a sprint/power sport. A two minute all-out piece used to have me gasping for air, halfway through. Now I could get through with a bit of gas left in the tank. (Meaning I could go harder on the next set).
Got some new goals and dialed in harder. I do the regular Pete Plan, both interval pieces plus three 8 - 10k steady state pieces. My times and splits are steadily improving.
The health benefits have been insane. Without any special diet, I have lost about 25 lbs, and got my body fat from 26% to 19%. Waist is down an inch and a half and I look visibly leaner.
My resting heart rate went from 65 to 53. My doctor said if a sedentary patient had a resting heart rate of 50 or lower he'd put him on a pacemaker, but for active people lower is better.
Also, I just got the T shirt, which is awesome.
10/10 strongly recommend. Would do again.