I HATED my Rock Tamers and sold them off. They worked fine in theory, but in heavy crosswinds, regardless of how tight you got them, the wind would twist and distort them. I couldn't believe I got more damage using them than I might of without them. The bolts on the top of the flap scratched the heck out of my bumper, and when in a turn the flaps would curl up in the wind and the nuts on the back of the fancy nameplate actually scratched the front of my RV!
I know each rig is configured differently, and some of the 5ers are low frames in the front vs high (mine at the time was high), so others may have different experiences, but to me they were just junk and I was sorry I ever tried them.
Ford flaps are working just fine for me.