I have no experience with B. I now have a 2013 S, but it has ECO on the shift lever as an alternative to D, just like my 2011 had. In the 2011 I used an illogical mix of the two modes, mostly because the car always went to D when I put it "in gear", and I often forgot to "double shift" it to ECO until the lack of go-pedal regen bothered me. But when I was thinking about it I used D on the freeway for milder off-pedal slowing, and ECO on city streets for more go-pedal control of regen.
The big difference for me in my 2013 is that it remembers whether I was last in D or ECO and restores that when I put it in gear, even across power off and power on. Now I drive in ECO all the time, even on the freeway, and never even have to think about it. I just use a very light pressure on the accelerator to slow gently as needed on the freeway. I prefer the additional control of power and regen that I get due to the longer accelerator pedal travel near the top end. And I still know that if I really mash it I will get just as much power as I would in D.
Ray