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.
On a rowing machine, you don’t want to be wearing clothes that are too baggy as the fabric can get caught between the seat and the beam it slides on. It’s not a disaster if that happens, but it can get annoying if your shorts keep getting caught there while you’re trying to get a serious workout. It’s better to wear shorter, tighter-fitting shorts (nothing ridiculous), but just enough to ensure it doesn’t the material doesn’t hang down.
If you’re interested in using a rowing machine for focused training — whether for outdoor rowing, an indoor competition, or as part of a larger fitness program — you’ll want air resistance. If you’re drawn to rowers for the enjoyability (alongside the full-body, cardio-plus-strength training efficacy) of a rowing workout, consider a machine with water resistance.
If you're looking at a WaterRower, you're probably also considering the Concept2. They're both great machines, but which you choose depends on your needs. I think the WaterRower is ideal for most people, but not everyone. The WaterRower has a number of advantages vs the Concept 2 - it is quieter, the mechanism up front is lower profile, it has a comfortable seat, it is much better looking, it's easier to stand up when you're not rowing and it's just ... zen-like. There is something about the smoothness of the WaterRower that makes it a joy to use, and because it's quiet you can easily stream your favorite binge-series without cranking the volume too high.
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.