Wow, that is not a clear sentence. I can understand why you cannot understand it.
You are right: A BOON is a good thing that happens at a perfect time.
"I passed the test! It was a real BOON when the teacher gave us extra time."
"Good weather was a BOON to the people looking for the missing child."
And you are right with BIG BROTHER: The term comes from Orwell's novel 1984. "Big Brother" refers to the government watching people too closely.
So this sentence means to say:
Location technology will not become a boon, a wonderful thing for everyone who uses it, OR become a bad tool for the government to watch people with, UNTIL it becomes better.
Right now, the technology is not a BOON, a good thing for anyone, because it does not work well, AND
it is not an evil tool for the government.
But later, when it works better, THEN it will EITHER be a boon for all of us, or a bad tool.
Not a clear sentence at all.
(The author was trying to alliteration, where words start with the same letter/sound... Boon or Big Brother.
For example, Higurashi hoped he'd hear how Herman handled his hamburger.
Sometimes alliteration sounds good, but other times it just sounds silly.)
Student or Learner