I agree with the previous reviewer. I used these studies when I was first learning piano and they helped me to progress with fingering and sight reading. They consist mostly of short scales and five finger patterns which are kept interesting by the harmony. Each study teaches one or two tricks, of fingering or of coordination. These are appealing without the difficulties of both hands at once. Later studies gradually introduce more left and right coordination. Some of the harmonies remind one of Bach, or other Baroque compositions.
I highly recommend these to anyone who is looking for first pieces to learn. Most of these exercises play one hand at a time alternating back and forth between the right and left hands. The hands share a few notes here and there introducing the player to the skill of playing with both hands. A couple of the exercises do play both hands simultaneously but they are very easy pieces and come together very well. I just can't recommend these highly enough to someone just starting out, especially if you are a self-learner. I don't think you could find easier pieces anywhere that sound as interesting as these pieces. These 12 little etudes helped me to start playing very quickly one hand at a time by the process of alternating between the hands. I only wish Kohler had written many more of these little gems.