Kg/min
The CI dimensions are Kg of fuel per minute, but it is not fuel flow. It is a coincidence that 320s cruise fuel flows are in the range of 40 kg per minute.
Airbus says that in the 320s I fly, a 40 CI inserted in the FMGC will give us cruise LRC, approximaly.
Canuckbirdstrike
I think it doesn't make any difference when you are comparing the results of changing a CI or mach number. If from then on the result is better in fuel and time, then flying at that MN is better.
agree in the other things, specially the second point. I think it is really difficult for many airlines to come up with the real CI for each city pair. The money they would have to spend in calculating those CIs and updating them frequently could render the savings useless. Ormaybe they just have idiotic management.