Replacement "exhaust systems" which means all the pipework and boxes starting from the end of the manifold (or downpipe or catalyst) backwards, are available from different manufacturers in a choice of materials, tailpipe designs, flow efficiency and noise characteristics.
Catalyst Converters - Required by law on all UK cars first registered K and later. High flow cats and de-cat pipes for racing use are available from a range of manufacturers.
Stainless Steel, this is an 'exotic' material being used in a rough environment, it needs to be well engineered to live up to it's promise of long life.
Life-time Warranty means - while the car remains in the ownership of the system purchaser. Most stainless steel systems come with a Lifetime of ownership warranty.