It's just 2 diffusers. You can use 2 in the front, or one in the front and one in the back. The Edge has a huge front end, so I'd use 2 in the front. I didn't put one in the back, even though I have 3 of them in my garage. I had one on the back of my last truck, and I never once got shot in the ass with laser for 5 years, yet every time an Infiniti was behind me, the lane change thing would set it off the whole time...
I'm not one that bashes other people's stuff, but, if you want to know my personal thoughts, look at what I have installed on both of my cars.