We have it on our coupe as standard, it does sound good and it's nice that it's switchable, but not sure I would have specifically paid the extra for it over other option choices.
2015 R172 SLK55 AMG, 2018 BMW 530d MSport xDrive, 2018 Mini Cooper S
Don't think it's that important as an option on the C43, but the dealers will tell you that its almost a must on the C63 saloon and estate for resale. (Bit like Porsche and their sports exhausts).