GSF = German, Swedish & French car parts, an aftermarket parts supplier here in the UK. I imagine the cats are aftermarket. I wouldn't fit them.

How old is the car? You should get 60k to 120k miles out of your cats; they are a long term wear and tear item. You wouldn't fit cheaper and smaller brake pads just to save money, so why fit cheaper and smaller cats?

General opinion on this forum and all the others is (1) aftermarket cats are smaller and as a result don't last as long as OEM and (2) the car will never run right with aftermarket cats because, being smaller, they behave differently and send different signals back to the engine.

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190