This was a combination mandolin-guitar that allows you to play mandolin music while playing the left-hand fingerings like a guitar.
It was tuned like a regular guitar, but an octave up. A mandolin is tuned in fifths.
During that era in Italy, mandolins were all the rage. Different regions developed their own variations of mandolin, with a differing array of strings.
It sounded nothing like a mandolin. Instead it had a big jangly sound especially when amplified through a Vox AC30.
Back in the day, the Mando Guitar was not a hit for Vox since no artists of the day endorsed it. Although this advertisment states George Harrison played one. Brian Jones played one too.
The only guitarist I have seen use one is Buddy Miller. I saw him and his wife Julie at a local club and Buddy used it on one song.