E61 M5 exhaust mod - yes or no?

[ant123456]

This guy seems to have done a fair few of these now.

What do you reckon, worth a go? My only concern is that he has to cut the rear boxes off to mod.

My car is under BMW warranty so makes me a little twitchy.

http://www.ebay.co.uk/itm/181644592491

[ant123456]

Don't want a after market exhaust, bit to much for a everyday car with 2x kids in the back.

This seems a more sensible option plus it's reversible