Despite the differences in the size as listed in the descriptive reviews for each of these two bullets, both the bullet and the handpack are exactly the same size and shape. If I had to find a difference, the cord on the Doc Johnson Black Magic Bullet is 1/2″ shorter. Otherwise, they are both plastic bullets with 4 settings and they light up the same. The Harmony Bullet is shiny, slippery plastic while the Black Magic Bullet is “velvet cote” plastic. They both take 2 AAA batteries and the bullet motors are almost identical.
Always clean before and after use with professional adult toy cleaners.