We find it brilliant - especially in airports (and big shopping malls). First of all, it keeps the older toddler/child "contained" so they don't wander off and get lost; it saves tired legs; you can get from point A to B much quicker than with a trailing child.
Sometimes we have the 1 year old in the push chair, the 4 year old on the buggy board, and then the 6 year old jumps on too! It's probably not meant to take the 35kg of their combined weight, but it hasn't broken yet! Obviously it's heavy to push with all the kids on board, but it's fun! Lots of people smile and point as our "choo choo train" rolls by!