As for longevity, I'm not sure how the Macs handles heavier children, but my 14mth old is already 30lbs and the Callisto steers so easily (one hand also) and I don't feel his heavier weight. I compare this to a Silvercross Fizz which I loved for mall shopping until recently... I feel the weight when pushing him and steering now requires 2 hands. I've been pushing both since he was about 20-22lbs.
HTH