Dont do it! It'll be a "Pig in a Poke!" Save up a few more pennies and buy something decent!
Most swear by Scorpion or Milltech or Buddy Club or Japspeed or Nismo or .....!
Just NOT a cheapy Fleabay!
japspeed is cheap ebay tat
£450 is a good price for a custom exhaust, is it full stainless?