I still have my Magical Musical Thing! It was a long blue stick the size of your whole arm with multi coloured numbered 'buttons' in two rows. It took a 9 volt battery and was really high pitched. I still have the music books that came with it and could play them all like "Home on the Range" and "God Save the Queen" and loads more. Sadly my Magical Musical Thing broke after too much use only a couple of years back. My son played with it but now he plays the piano.
Magical Musical Thing was made by Mattel in the late 1970s. It came with a Magical Musical Thing Songbook so you could follow the coloured button insttructions to play a real song rather than just dab your fingers across the keyboard or, as the boy in the advert did, rub it across your forehead!