Hmm I see a bit thinking that reminds me of my own thoughts. When I was first getting into modifying cars I figured an engine that is N/A can only ingest so much air so opening the throttle more or faster does nothing.
Then I talked myself into going from a 55mm throttle body on my volvo 744 16v to a 65mm throttle body. I was fairly certain it would do something good, but had to find out for myself. What it did was made the throttle much much more responsive. Much like putting a pumper carb on a dirt bike that had a constant velocity carb or wrapping some extra pvc around the throttle cam so the throttle opens faster. Throttle response is right now. While total power output isn't improved, the increased response makes for much more amusing driving.
I figure the eco mode might be good when I'm in the woods climbing snowy trails and trying to control wheel spin on a manual outback with no traction control. We'll see how it all turns out, I'll be ordering one. In reality it's a pretty cheap way to get some more amusement.