OK, so I've only got a few miles on the car but the air suspension is fantastic ! Very compliant, smoothing out the bumps and providing a plush, luxurious ride (it's better than the wife's GLC on bumpy roads but don't tell 'er...). You can notice the difference when you change the mode to 'Sport +' too, although the other options (sport, comfort & eco) don't make a lot of difference in my humble opinion. Worth the extra ? Probably, but mostly because I went with the 'off road' package where it will make a big difference over springs. I guess if you do a bit of towing it would make a lot of sense too. I shall update as I get some miles on the old girl (that's the GLC not the wife...).