I enjoyed this story. As others have said, the narration was spot on, and the style of the story felt very authentic.
My comments - with the inundation we've had with American politics lately, I'm surprised it took me until today to make a possible link to Red / Blue -> Republican / Democrat. The thoughts of a chip manipulating political preferences is scary...
My understanding of the story was that the chips didn't make it that you *couldn't* have 'off-brand' things, just that on-brand items were better / gave pleasure, etc. Makes you what would happen if someone mislabelled Jif as Skippy, etc. So, the Black chip wasn't there to make the Underground groups, but to tap into / exploit them. Make sure that they buy the 'right' underground things.
Another interesting thought is what hackers of that world have done - obviously something, since its become illegal to 'tamper' with the chips. Think of the damage that a virus hitting the chip. All the sudden everyone becomes vegan....
But the scary thing is how manipulating preferences could be used to modify people's personality. Start a campaign where people stop liking risky behaviour, prefer consuming entertainment to producing it, where they prefer reality TV to political issues. The fact that school subsidies were linked to kids being chipped means that they have access to the kids when their personalities are being molded, and that they are at their most vulnerable to peer pressure.