There are 3 main companies producing lower cost powerbocks for hobbyists. Fly Jumpers, PoweriZers (now also called PowerStriders) and Pro Jumps are some of the range of identical models produced by one company in China. Poweriser brand powerbocks are produced in Korea. 7 League Boots are produced by an Austrian company and are the most expensive of the non-pro brands.
...is this true?
That sounds very much like something I wrote, or plagarized from something I've written, so yes it's true
Just over 6 stone is about 39-41kg, which means he's right on the border between the F30's (30-40kg) and F40's (40-50kg). I'm assuming as you mentioned pink you are considering buying the junior pairs, and he'll need F50's ideally.
How tall is he? If he's under 5ft there is no point in buying him M60's (Adult frame) as he won't be able to use them. Between 5' and about 5'3" you'll need to make a few modifications for him to be able to use them, which basically involves raising his foot up by placing a platform on the footplate (Where you stand). This can be done with wood, flip-flops, really whatever you have lying around that will provide a solid even surface that can be fixed down. Over 5'3" and he'll be able to use adult frames no problem (although at 41kg that'll make him really thin, so you'll have to pad out the kneebars for him using pipe insulation, or get calf cuffs).
Having no idea of his size and a rough estimate on his weight, I'm going to suggest you go for the F50's, junior pair. HOWEVER, I think that George should wait until he has grown and fits the adult frames. The junior bocks are no way near as bouncy, and due the shorter spring with sharper curvature, it means the springs are a lot stiffer and harder to use. However, if he wants them he can learn on them and then progress to the adult frames when the time comes, I think he might just be a bit dissapointed with the kids models though.
Sadly I can't link to other sites due to the forum policy *shakes fist at webmaster* so I'll send you a sneaky PM with a lot of info