I bought a set of Cobra slip ons, discounted due to being shop soiled, nothing a polish did not fix, came through no worries, its my third OS purchase of exhausts over the years, never had any issues with them.
As for the O2 sensor it is further up on the header pipes so the slip ons have no effect on them working at all.
The brackets are made exactly to fit the 1700. the dealer is talking BS. he may have had problems with other aftermarket pipes, but I can tell you the 4 inch Cobra slip ons with the scalloped tips fit fine.
Price? $440.00 AU delivered.
I will say the Cobra's are loud, I packed mine with a material I found on the web to quieten them down a bit.
go for it. they are a snap to fit.