Latest rumor I read was that it was going to ship with Linux (if you google steam box linux you'll find some sources). Price, I haven't heard anything about.
As for advantages, it's probably the same as any other console, which means it comes with the same disadvantages. There will probably be steam box approved games on steam, which you will be sure will work in it, and you may also see some developers targeting it specifically.
But yes, if you know what you're doing, there probably wont be any advantage on choosing this over your own custom built PC. I don't see many developers restricting their games to steam box.
As for advantages, it's probably the same as any other console, which means it comes with the same disadvantages. There will probably be steam box approved games on steam, which you will be sure will work in it, and you may also see some developers targeting it specifically.
But yes, if you know what you're doing, there probably wont be any advantage on choosing this over your own custom built PC. I don't see many developers restricting their games to steam box.