It's not useful because nobody has one. Google have yet to "do" it. Their self driving car is as useful to anyone reading this as human teleportation right now. They're great idea's but until they are accessible in some form to the public, it is still just an idea that needs work not an innovation.
I look forward to the day I can say I do have one though.
I look forward to the day I can say I do have one though.