Car seats for the quints?

I think the strap you are referring to is the one that tightens the harness against the baby's body. I would not buy a car seat unless it had that feature, because the harness has to be snug against the body, but it is next to impossible to put them in when the harness is tight. That strap will allow you to loosen the harness to put them in and then tighten it once they are buckled.