Yoshi. I put a carbon TRS on my K5, pulled the wire as per instructions and no FI light. The yoshi is lighter than the stocky and of course sounds sweet. If there was any loss of bottom end from removing the SET it is neglible. Will get the AFR's checked when I can.
One thing I read in the instructions was to repack the carbon can every so often, 15K miles or so, not sure if its going to need it it or not but I wouldn't be looking forward to drilling the rivets out.
i bought the TRS yoshi slip on today and i noticed power increase everywhere. from my experience, with slip ons you dont really notice the difference. i noticed a pretty good difference with this pipe. it sounds exactly like the stock exhaust too. its a little too quiet for my taste, but it flows good.