I bought this for my nephew both as a thank you gift, as well as to help him since he is trying out for varsity baseball. This is a terrific tool, especially for him, because he wants to practice being either a pitcher or an outfielder. This device help both at the same time.
The concept is simple, throw at the red box and the ball bounces back to you somewhere between a 30-45 degree angle, enabling you to catch some good pop-up balls. Though some energy is lost in the physics of the ball bouncing and reversing velocity, it basically pops back to you. If you throw it too high, then the angle is deflected higher and you have to scramble to catch that fly ball. If you throw too low, it comes back to you as a grounder (great if you want to play shortstop).
The best part about this is that you can play by yourself as long as you want. A pitching machine means virtually the same pitches each time, and you must constantly reload if you are by yourself. If you want to stop in the middle of pitches, you will inevitably have balls to chase. With the pitching net, you only catch what you throw and unless your aim is really bad, you can play for hours with a single ball (hardball or softball).
As a pro tip, if you are as bad at throwing and catching as I am, stand close to the net and practice lighting tossing at the red square. They say practice makes perfect, but in reality, practice makes habit so only perfect practice makes perfect. Hone your technique and aim at shorter distances, then over time start stepping back and increasing power -- all while maintaining your aim and technique. Practice correctly and you can expand your range later with less effort.