http://millteksport.com/exhaust.products.cfm?variantid=1554 For the B9 S4 / S5 it looks like Milltek have three options: Cat bypass / Test pipe Milltek downpipe using 200 cell HJS core HJS EC Approved 200 cell downpipe Its obvious the cat bypass is illegal for use on the road so I will skip to the other two. The question is... Is the Milltek 200 cell cat still UK road legal if it isn't EC approved? Will it trigger a C.E.L? Will it invalidate insurance even if declared, as it's a non compliant part of the emissions system? If the answer to any of the previous questions is yes, what is the point of it even being developed and sold, as the only sensible option is to buy the HJS EC approved version for driving on the street? I'm confused as both the Milltek own brand and HJS item seem to be using the same 200 cell core, one has some heat insulation and the other not. So is the 600 quid difference purely down to the HJS own brand one having undergone the rigor of approval?