The Safety Struts are not the end-all, be-all solution. These OEM bumpers are just too thin. I installed the Safety Struts on the back of my 5er, and with only two bikes and one trip, the bumper still twisted like a Twizzler. The welds were "fine" but the bumper itself would have crumpled in short order. Uninstalled and returned the Safety Struts.
Paid a local welding ship to gusset and install a 3/16" thick bumper. Problem solved. Traveled thousands of miles, with up to 3 bikes hanging off the rear - no issues.