Handlebar is a great addition to Ninebot by Segway miniPRO. Although knee controlled bar is nice for the younger riders many prefer to have more stable and reliable way to ride and decide to upgrade for handlebar option.
It is important to understand that once handlebar is installed your miniPRO turns into almost full scale Segway (for 1/5 of a typical Segway price) and it will behave that way. The only reason why Ninebot by Segway miniPRO is self-balanced when a rider is not riding it is because the knee-controlled bar is located in the middle hence the center of gravity is in the middle. When you install a handlebar your miniPRO will behave like a normal Segway.
When your machine is not in use you should either use a parking stand (front facing) or lien your machine in front of a wall. Just don't leave it unattended.