Gti6 cat advice

[GtiJimmy]

So my replacement originl cat was 'lost' in the post which may or not be true but its stitched me up a bit as I was relying on and prepping for that. So i went to exhaust specialist in wembley - powerflow- and they are offering a 200 cell sorts cat for 300-350, or a 400 cell one for 250-300 pending on labour etc. The brand theyre offering to weld into my drop pipe is magnaflow, my question is does anyone have good experiences with this brand? Also as this is the round ( kind of cocktail shaker looking thing ) as opposed to the flatbox mirroring the original. Does anyone know if a 200 cell of the round type would work well with the rest of the exhaust system which is orignal parts from Pug. Or should i go for a 400 cell flatbox ( aftermarket imitation of the original) . I only ask about the shape as im aware of a few people saying that its shape can really affect the back pressure etc. Should i go for magnaflow? Not surr if they do other brands part from their own custom ones? Any advice would REALLY help as im using google for all my exhaust knowledge and thetes nothing netter than the real thing

Thank you