Don't know why, perhaps due to rising demand and production bandwidth, but be forewarned quality control is an issue. Assembly is easy enough, though have gap where back separator does not fit snugly after tightening nuts as firm as they will go (see pic). No water level sticker on tank received, so had to measure water manually according to calculations (4 gallons). Siphon was not air tight (even though release valve closed firmly), so had to manually pump instead of siphon. S4 monitor only flashes, not working as of yet and now have to take a apart top of unit to figure out why, currently not resolved after verifying connections and looking at simple solutions on website.
Noise level is another large factor that tips the scale more towards water rowers. Air rowers make a fairly loud “whooshing” noise every stroke, which makes them bad for people who like watching TV, have sleeping children, live in apartments, or like working out early in the AM. Water rowers do make some noise but the splashing of water in the tank is a lot quieter and more soothing than the fan noise produced by air rowers.
 The amount of water in the tank simulates the weight of the boat and crew, the more water in the tank the heavier the boat and crew. The standard Calibration Level is Level 17. If the user is lighter in weight, Level 15-16 can be used. If the user is heavier in weight, level 18-19 can be used. The maximum level to fill the tank is Level 19. DO NOT fill above the maximum level – this could void the warranty.

The WaterRower Natural is outfitted with a Series 4 performance monitor that's designed to balance technical sophistication with user-friendliness. The monitor--which includes six information and programming windows, six QuickSelection buttons, and three navigation buttons--displays your workout intensity, stroke rate, heart rate, zone bar, duration, and distance. Plus, the monitor is compatible with an optional heart rate chest strap and receiver, which helps you optimize your workout and achieve your exercise objectives.