My 7 year old is transitioning to a booster with a back that includes a seat belt guide for the chest part (do they all?). After so many years of obsessively tightening, sitting in the durn thing to get the H clip in the right spot etc. it is feeling really weird to me that the seat doesn't actually attach, it's just the seat belt doing the restraining. Do I have this right? Are all booster seats like that (eg. not attached using the tether)?