A couple of kids on my road have them and they are annoying. They may be louder than my Ninja. The kids are dangerous on them too. The bikes themselves are too low to be seen clearly and will be top heavy due to your son outweighing the bike. Get him a mini bike or an 80cc dirtbike. It is more of a motorcycle experience and will likely be safer and more fun.
That being said, the pocket rockets do look fun.
“I am the best there is at what I do, and what I do ain’t nice.”-Wolverine