I found the installation instructions online. The front and rear pieces screw on/snap on/stick on to the existing front and rear body work (bumpers). It doesn't appear that they hang down any lower than stock, although they may just slightly. What is different for the front and rear, though, is the design. The lines are different and give a more "sporty" appearance. Plus the color is a gray-ish color to offer a two-tone appearance.
The side pieces replace the existing side pieces that come with the vehicle. It may be nothing more than for color matching the new front and rear pieces. If that's the case, and if the color matches your car already, you probably wouldn't need to buy the side pieces. That's assuming, of course, that you have any interest in them at all.