Couple of points. Bosal do offer two Cat ranges, a premium, prefixed 099 and budget, prefixed 098. Both have a two year warranty. Both cars we had noise probems with used the 098 budget variety. The Renault was in a very small casing about 4" square, 3" long. The Citroen is a much larger casing of conventional shape.
I agree obout fitting OE to post sensor cars. My reasoning for these cats is a 2 year warranty will at least get through the next two MOT's. A time period that will probably see the natural demise of cars this age.
Today a Fuel Parts cat arrived. The casing is about double the size of Bosal 098 unit. Car is queiter without a doubt, less harsh bit still a little boom. It still has Bosal silencer.