The O2 extended bung is already welded onto the HFC's but there was also an additional extendor (about 1/2 inch) included. It was a little too big to screw in though I I didnt install it. Not really sure why it was included. But I have put about 1k on my car since the HFC install and no CEL...so it must be fine.
As far as the best CBE...depends on who you ask (everyone reps there own pick). If you want to check out the Invidia Gemini review...here is my thread (
Invidia Gemini CBE & ERZ HFC Review (with db comparison) )