To me the main sensation of turning on EcoPro is that it feels like a 500 pound person just materialized in the back seat. So obviously starts are going to be slower and it takes longer to hit freeway speeds going up an on-ramp.
I did a little bit of checking MPG with EcoPro on and off and I couldn't really tell a big difference, which may say more about my math skills than anything else.
Since I have stopped activating EcoPro I have still been happy with the MPG, and the X1 runs the way I think it should. To each his own.