Consumer reports purchased the Boulevard and the Marathon and double checked the harness straps. Neither were fully secured. Double check before you install. They also point you in the right direction to fix them quickly and easily. :-)
"We bought one sample of each of the Britax Boulevard ClickTight and Britax Marathon ClickTight convertible car seats, and found that—with both seats—one or both sides of the harness strap had not been fully secured to its lower anchor hook."