Best Aftermarket Manifold/Cat for MK4 2.0 Petrol

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My mechanic has advised that the manifold/cat assembly has seen better days and while it's not dangerous or leaking it will need to be replaced sooner or later as the outer casing has deteriorated.  He also tells me that having done a similar job on a Volvo (which has the same engine) they ended up using genuine Ford parts as cheaper after market parts didn't fit properly.  Ford part is approx £450 + 2-3 hours of fitting.  Has anybody had any success with after market parts and where would be a good place to go for a competitive price in the Reading/North Hants area.