I went with these front and back. I like how subtle they are compared to the other ones out there. They came with a sheet that helped with mounting them. The rear ones were confusing at first, but it's three screws total. You have to remove clips from the carpet liner and use those holes for the screws.
https://www.amazon.com/Ford-Focus-ST-rock-guards/dp/B00R6UOPEO
Look the ZL1 guards, that’s what I got and I love the subtle look. Not as much protection as flaps but much less in your face. ZL1 Guards on Amazon