I have used this for a while, and in my experience the measurements didn't really fluctuate as much with the coffee type/age/roast as much as it did with the brewing type, water:coffee, grind, brew time.
<jumps on soapbox>
Using a Scace device didn't really subtract from the art of espresso, or phone back to big brother when someone goes outside the parameters. SO espresso shots outside the Illy parameters are still espresso, nobody gets hurt knowing where the lines in the sand are. The amount of coffee to water ratio before brewing is obviously important, why not the coffee to water ratio when you drink it?
<falls off soapbox>
Check it out, join the travel loop, curiosity only costs postage to the next destination. Skeptics especially welcome.