Do you find it useful at improving your MPG, or do you turn it off and have the engine running at the lights? 

Personally i find it a pain in the backside its terrible in stop start traffic cuts out to quickly, not too bad at traffic lights, doubt it saves much in the way of fuel, its primary function is to cut emissions, also with no engine running you have no air con and my C- max gets hot very quickly without it.

I switch it of in creeping traffic, 

Makes no noticeable difference to mpg at all.  Even official figures only give the SS models 0.1mpg increase...  I leave it on though, very rarely do any slow traffic and it works well at traffic lights.

 

Is there anyway to disable the feature permanently, or does it have to be turned off each time you get in the car? 

Has to be turned off each time.  But unless you do a lot of slow traffic might as well leave it on.  

8 hours ago, CLCC said:

Is there anyway to disable the feature permanently, or does it have to be turned off each time you get in the car? 

You have to turn it of every time, couldnt work out how to disable it using Forscan.

6 hours ago, TomsFocus said:

Has to be turned off each time.  But unless you do a lot of slow traffic might as well leave it on.  

Yea i just turn it off in slow traffic as said earlier it works fine at traffic lights