Dave I had mine done about a month or so ago by dynachip. He takes the old chip off and solders a socket to the board (if its a pre NNN ecu) and then puts the new map chip in the socket, you could if you wanted to just plug the old chip back into the socket and it would be standard again...... you wont want to!!!
so after a month, there is still a bit of a flat spot as you pull away if you dont get the revs high enough but its much less than it was. From then on its smooth and powerful, it goes everywhere in 4th and 5th and makes for much more relaxed driving. and overtaking at any speed is a breeze.
I went for this type of tune rather than a big block of power type but the beauty is if you want to change it in the future for something more aggressive Mike will just mail you a new chip
As for fuel consumption, to be honest I dont know I think its about 3-4mpg better, im getting about 34mpg but the problem is you cant help giving it a blast and I havent got over the fun yet to do a serious fuel check
best
Dave