Those long car seat strap covers usually do affect how the child's harness straps fit them and because they are so darn long, usually affect movement of the chest clip as well. Yes, they are considered after market and are not recommended. Use at your own risk.....with that said a chaffed neck isn't desirable either. One trick I used to use before the boys were in seats that came with strap covers was to right prior to tightening up the straps, I would simply take their shirts at the neck on either side and pull them over (and up a bit) to cover the skin, and then finish tightening. That way the exposed skin was covered without having to buy an after market accessory.