The One-man Band is worn on the body and will drain the character's Sanity at a rate of 2 points per minute. Each Pig or Bunnyman befriended with the One-man Band will drain additional 25 Sanity points per minute. With the max of 9 followers, this means losing Sanity at 227 points per minute.
The device lasts for 3 minutes (4.5 game hours), degrading when equipped. Once a character stops playing the band, the followers will only stay loyal for a few seconds. Pigs and Bunnymen don't immediately stop following and doing the player's bidding, which means that the player should use it at short bursts instead of keeping it equipped constantly, to avoid big sanity drops.
The One-man Band in real life is the name given to street performers, who play multiple instruments at the same time by moving their legs and arms. The sanity loss might be due to the cliche of people disliking these musicians, or the immensely tiring physical movement required to keep the whole band working.
Dropped One-man Band.
Wolfgang using the One-man Band to make Pigs aid him in battle.