The volley trainer is simply the Leverage band with cuffs on both ends. So if you order a complete system, you can borrow a cuff from the A.P. Belt and attach it to your Leverage band, and you have a volley trainer!
By attaching each cuff above the elbow of both arms and shortening the length of the tubing, you have a very effective tool for developing great volley habits. The concept of the “catch” on forehand volleys encourages you to react forward with your elbow, as you would to catch a ball. The volley trainer keeps the elbows out in front of the body and resists the tendency for the elbow to react into a backswing. To drive the backhand volley, the volley trainer encourages you to extend from a bent arm to straight to make contact, while resisting the tendency to swing from the shoulder.
The volley trainer is sold separately and is not included in the complete systems.