Been looking at one of these for my RR TDV8, mostly because you can take it out before any main dealer firmware upgrades, then replace it when you get it back!
I once had a disco chipped and it kicked out loads of black smoke when you put your foot down. These say thats old news and this problem is now sorted. But i also work in sales!

http://plugndrive.co.uk/ then scroll down and click on Landrover logo