"The thing seems like junk."
Mine works great, and so do one owned by many other people. I was skeptical at first, and even though the LCD color doesn't match the red of the rest of the interior lights, I'm happy with it.
"do i have to buy that"
No. You don't have to buy anything you don't want to. Metra offers other kits for the G6, but you'll lose the DIC info without the 99-3303.
"I know Scoche used to make it and it looked like it was perfect but they stopped producing."
You can still find it by searching Google or eBay. However all the reviews I've seen on this forum at g6performance.com show that the Metra kit is preferred.