The Concept2 Model D is the ultra-popular air rower that you’ll see at most gyms. It is one of the best home indoor rowers you can buy period. Expertly constructed and ergonomically unequaled, this rowing machine looks great and rows smoothly without so much as a jarring catch. As an air rower, the Concept2 employs air baffles to create the resistance. A nickel-plated chain pulls the flywheel and you get your workout by pulling against the increasingly higher air pressure that the fan is creating.
Although some rowing machines are made of space-age, super-sweat-resistant metals, you still want to wipe off the equipment after a sweaty workout. These machines are usually constructed with a lot of various materials and salty sweat can be very corrosive. Keeping your rowing machine clean can go a long way toward extending its life, and its appearance.
I kayak (ocean and flat water, not river), so I was drawn to the WaterRower over a flywheel type rower (which I have used in gyms) because I wanted to hear the sound of the water, which I miss hearing against the hull of the boat during the winter when I can't get out on the lake. I also like the way the paddles engage in the water; it's a very smooth pull and release, and moving the mass of the water instead of a dialed down tension feels more natural. As someone else also commented, the seat (at least on the wood version) is incredibly smooth and solid; no wobbling at all. I generally listen to music on my Nordic Track ski machine, but with the WaterRower I am content to listen to the sound of the water; working out on this is somehow both energizing and calmingly meditative at the same time. In the event that you want to use it while watching tv (this is one use to which I wanted to put it), it is quiet enough to hear the tv without having to turn it up.
From a fitness perspective, the WaterRower Natural works 84 percent of your muscle mass, helping tone and strengthen your muscles while burning far more calories than most other aerobic machines. The exercise is also low impact, as it removes all the body weight from the ankles, knees, and hips, but still moves the limbs and joints through a full range of motion--from completely extended to completely contracted.