I bought both of my boys a pair of these about 6 months ago. I was kind of afraid of spending that much on shoes. But they had really been wanting them, and need new shoes anyways.
They have held up very well. Most shoes don't last them that long. But they still almost like new. At this rate the will out grow the size before they wear out.
It only took them about 48 hours to figure out how to Heely and walk in them. Walking had to been learned to because they have to step on the wheel. We went to Heelys main site and watched their online video that they have to help you learn.
You can buy replacement wheels, but we haven't needed to yet.
I ended up having to buy my husband a pair to. They kids enjoy it when he heelys with them. Really though, he saw how much fun they where having and begged for a pair too. I'm next on the list to get a pair, but i haven't found the purple ones I want on sale in my size yet.
On the kids/youth shoes you should go one size up from what they normaly wear. When I was shopping around, I noticed some sites tell you this and others don't. I sized up on the kids and they fit great with a bit of growing room.