My DD has just turned 10 and we still use the booster seat with a back and a harness , although one of the bigger ones. She's small for her age and fits well into it and much better than with the belt, thus it appears to keep her more safe.
She's not happy however with being fastened in all the time and wants rid of the car seat as some of her friends travel without a car seat at all and all but one other uses a belt. Most are bigger than her and I still don't think it's the safest for them, but I'm not going to challenge other parents choices as some is affordability etc.
Am I being unreasonable in keeping her in the harness or should I relent with her peer pressure and let her have a backless booster seat? What do you all do with your DCs and when did you move through the options?