We're about to upgrade to a Britax Marathon from a snugride. Snugride is installed with the belt, and we got it done at AAA at a car seat check event. It was totally rock solid, nothing can move it. Without ever touching the belt, its already loosened up quite a bit and I've had to tighten it a couple times. I've heard that seats tend to test better when installed with the belt rather than LATCH, but I'm sort of second guessing that because mine loosens up so much over time. So, is your seat installed with the belt or LATCH and why?