My fiance's son is a bulky kid for his age. The last time I weighed him was last winter and he weighed 60 lbs. I don't know his height right now, but because of him being so broad just doesn't fit well in a lot of harnessed seats. (GN) He is very broad and top heavy. I have had issues with a lot of hbb leaning when he is in them. If I lock the belt tight it helps a little but not a lot. Anyway... his HBB we have now doesn't really do it. We don't have his son every day, only one evening during the week and every other weekend. His mom's house is 15 min from our house on rural country roads. He only rides one way with us as his mom picks him up. He will be 6 in December. He has used a NBB before and sits well in it. I had insisted with my fiance he needed a HBB so we used that up until recently. Since he doesn't ride in it all the time and most drives are within 10-15 mins would you be okay with him riding in a NBB with us. For long trips where he may fall asleep we would def. use his HBB. He doesn't slouch and he sits properly. Belt fits him great as well.