As @Big Rat Paul referenced above I contacted TWG who were very helpful & who confirmed that the Quicksilver Exhaust (being only axel back & not containing any sensors) does not invalidate the warranty. There is a thread covering this where I posted TWG’s email to me & It applies to everyone with the system fitted to the RCF not just me.
Lexus Cheltenham, who are a brilliant dealership run by car enthusiasts, fitted my exhaust, along with a few others on here. So if you want to be belt & braces about it give them a try unless you can persuade your local dealership to do it.
Cannot say enough for the Quicksilver system, as @B1RMA said quiet as standard unless you prod the throttle then it sounds fantastic. It is louder on start up but reduces as soon as you put it in gear,
Best decision I made as it means I can drive based on the engine revs, which is something I missed with my previous ISF.
Go for it you won’t regret it👍🏻