While the dealers suggest this software update magically fixes all the problems(why now and not the last four attempts?) if you were to have the update on your car I would get the emissions checked at an independent garage and have it’s power measured on a rolling road as they can not do what they are suggesting without drastically altering both factors and I would not be happy about paying for a car that is 20%+ down on power and has poor emissions/economy compared to the figures when sold.