Like I said this is not a just a one bolt and go type of thing. But there are some instances where it will be great. Such as:
If you are riding somewhere a few miles away (Grandma's house) and the child wants to have their bike when they get there.
Camping, We take our bikes when we go camping and do quite a bit of carousing around on them. But there are place around camp that the kids can ride and some further away that they can't make it. In this case the Buddy Bar will be handy that I only have to carry one bike.
There are a few instances where carrying the tire and being able to switch back to the bike will be handy. But for the most part it may be best just to leave the tire at home and save the weight and hassle and use just like a trail-a-bike.