It might take a few shoots to get accustomed to the movement of dropping the washer, stepping on it, drawing the string tight and then shooting. With practice, however, this initial set up will become fluid and natural.
The string tripod also allows for a lot of flexibility. The height at which you take your picture can be easily adjusted: keeping the string taut, you can wrap it around a wrist, or bend it to the side with your knee. To raise it higher, just attach the washer end further up your body, perhaps to a belt loop and then doubling back the string. Really, you can attach the string to anything; a lamp post, a tree, a chair, whatever you can think of, for unlimited angles and heights. All it takes is a little patience and a little creativity, and this easy way to reduce camera shake is yet one more tool at your disposal.
To prevent the string tripod from tangling, the best solution is probably to just wrap the string around your camera when not in use. If the build of your camera prevents this, then wrapping the string around a wrist or wallet or even around the washer itself between uses might help prevent tangles. However you decide to coil it, make sure that it can easily uncoil as well.