I did some quick calculations on this awhile ago (might've even posted them here based on a archived article) and it's certainly possible. Hell, it's not even incredibly difficult to create a blimp.

What they do end up doing, however, is being big. Very big. Makes parking them a biatch. However, it would be very cool to be able to take a leisurely float down to the Caribbean and just hang out there.

As for pirates, maybe having some .30cal mounts in case on of them realized what an ultralight could do. Or punctures to the structure.

Heck, you can fly off with a lawn chair and a couple of weather balloons, as some amateur inventors have proven. Things get more complicated when it comes to doing it repeatedly and without crashing, though.

True - and what these guys have done is develop a system that sucks the helium back into storage tanks rather than venting it. Makes it much easier to control.

My guess is that it's not all the difficult to do in concept, but the actual doing of it in a manual sense is probably somewhat of an art form. Then automating it so that one just points a joystick towards where they want and the system does it automatically is probably much higher - and I think this latter portion is what they've done.

That would be a waste of energy. All you have to do to control your altitude is reduce the volume of the gas-filled area using ballonets, same way a submarine uses ballast tanks to control its depth.

Honestly, it could be that. I'm not sure as the site wasn't particularly clear on the details. Probably afraid of competition or some shit.