For some people, the thought of cardio just makes them turn right off the thought of exercise. Yeah, I can understand that, but when I have people come to me with that statement of hatred toward cardio, I often ask them if they have ever used a rower and the answer is usually no. In the next minute I can't get them off it.
Rowing is unique for cardio vascular training because it heavily features the upper body as well and the lower body. This means a higher calorie burn. Smart eh? Ever seen those guys and gals in the surfboats, all of them extremely fit. I've often admired them for their physiques. The combination of upper and lower engagement while rowing makes this exercise a no brainer for getting your body in shape fast. Because of the low impact it has on your joints, this means it can be used by all types of people from young, fit, older, and beginner. The best part, there is no difficulty to the exercise so you can jump on and use the rower straight away.
In the gym I always recommend using the rower before any workout because it's a fast way to increase circulation around the body and have all your muscles warmed up before you do a workout. Makes sense right?
As for convenience, it's a pretty compact piece to have at home. They either fold in half or you can just stand them on their end. You can't do that with a treadmill. It also means you only need one person to move it as well. If I was going to recommend one piece of equipment and you are short on space, the rower should be at the top of your list.