I was given the Step Caddy for Christmas, and haven't had the chance to use it until recently becasue of the weather. But I have to say it is really oool. And it really works.
We were on a walk with my son (3), nothing too serious, just a nice walk, pretty flat, on paved and gravel paths, we were walking and he was on his balance bike. Towards the end he hit his wall and wouldn't move. I ended up carrying him on the Step Caddy, and carrying his little bike too. It was so easy. He was so happy riding on my back, his mood rebounced and he got all chatty all the way to the car. The day was saved. It was so awesome.
The construction is really solid. I don't like the g-hooks they use, but once you work them out you can see why they use them. they are really solid and safe. I think the magentic buckles are the coolest part, they make it very easy to clip his harness in, and I can see them without straining my neck. The buckles just attach and lock in, you hardly have to do anything just guide them to right location.
I wish it would be even smaller when packed up. But it is still pretty small and I shove it at the bottom of my backpack.
In summary, it's great, we love it. I am sure we will use it more in the future, more than just hikes. I hope this helps.