The UK doesn't recognize it as a sovereign nation, and would treat any activity there as if it were in the UK. Sealand is just marketing, it's a false sense of freedom from laws. I would rather host in Russia, or a non-friendly (to the US) country. They openly don't give a shit about UK and US copyrights, a lot more safety than betting on the UK not taking a boat out a couple miles at the request of **AA.
All the sats circling the globe are owned by companies mostly in big nations, you still don't have any real autonomy out on that platform since they can simply shut down your link. (same goes for fiber or whatever kind of physical connection).
At the price they are offering it, it would make more sense to buy a big fucking boat, or maybe buy an aging oil platform that is way away from any territorial waters.
Or, buy one of these... http://www.cdnn.info/industry/i041207a/i041207a.html