that button is actually a bar or flat plate that slides so it will play two different keys which is nice for stepping
My old chromatic is my favorite even though the wood is starting to split just a wee bit.. Since I play while playing my guitar mostly, single notes are a bit hard as opposed to a chord. I'm self taught and play by ear and play well when the mood hits me....I don't play well on demand....but then I'm not a professional musician.
In my teens, 20's & 30's I would take one camping or fishing with me and was when I enjoyed it the most and the gals sure liked it.