Diono Monterey 5iST FixSafe High Back Booster Car Seat with Expandable Height and Width, Compact Fold to Full Size Booster, Foldable, Portable Booster for Go-Anywhere Travel, Yellow Mineral

The concept is good, and I love the travel/foldability of it. Unfortunately it takes design cues from general clothing sizes of small, medium and large - meaning if a child had a tiny waist, he/she must be short. Or, if tall, they must be extremely wide. The height and width expansion cannot be adjusted separately. There’s no option for *just* raising the height. To accommodate a child 48” tall the kid probably needs to be 60+ pounds. My high school son, obviously too old for a booster, is 5’6” & 116lbs of muscle didn’t even come close to needing the seat expansion at the highest headrest setting. The idea is ok, but clearly designed for todays *ahem* “larger” children, not super slim or even low-average BMI kids. FWIW, I’m 5’7” and 140. I fit in the seat width wise. How is it supposed to fit my 1st grader who is 100lbs lighter than me?!?My kid is thin, 48” and 40.5 pounds soaking wet. She *barely* meets the regulation weight for a booster but since our car got the best safety rating I relented & said she can use a high back booster in that car. I regret it. Returning it. I need a thin, slim seat to fit in a model 3; one safe enough for local streets (under 45mph/to - from school) - this was almost perfect but not quite.