Eco mode turns down the aircon, disables cornering lighting, sets the ACC to slow acceleration (which I'd argue is quite dangerous) and deadens the throttle response even more.
What sort of extra economy are you getting for doing that?
If you are frequently flicking to S and then hoofing it, you probably are burning up whatever you've saved too...
I remain unconvinced...
I'm sure for VW it takes ~1g of CO2 off of the official figures (which is worth a lot to them) but for you and I?
Don't get me wrong, I'm all in favour of low pollution and better pound note savings, but maybe not to that degree!