I'd be curious as to how much gas it really saves. The real gas consumption is accelerating away from a stop. I think it would have to sit for a long time to effect mileage enough to be worth it.
One question I have had - I assume the A/C quits blowing cold air - is this correct? BTW, I'm glad the 550 does not have it yet.
2012 BMW 550 M-Sport
2015 Audi A7 Prestige
2014 Lexus GS350---Wife's car
2013 BMW 1600 GT---2011 Kawasaki Ninja 1000---2012 Ducati Panigale