As a third-year owner of a Gaggia MDF Coffee Grinder, I'd like to share a few of my not-so-secret tips for using this machine.
Since this machine has 34 settings, I'll save you quite a bit of time (and coffee) and say that the best grind setting for espresso is going to be right around a number 6. Of course, there are going to be variables to this setting, based on the type of coffee or espresso machine being used; but a 6 would be a good starting point. You'll be able to adjust up or down a number or two from there. The first time I used the MDF I started at the halfway point, around an 18, and then adjusted down one setting at a time from there. After a well-spent hour of my life, I can now share my experience with you in hopes that you'll have a quicker and easier time dialing in your MDF.
I also know from personal experience that this grinder can actually grind too fine, basically turning your coffee puck in to cement in your portafilter. Quick word of wisdom: Don't run your espresso machine for more then 10 or 15 seconds if there is no water coming out of the portafilter, as you run the risk of ruining your pump...not that I've ever done this before or anything.
I use my MDF once a week to grind a pound of coffee for my drip coffeemaker. As most people know, drip coffee requires a courser grind than espresso. In this instance, I find that a 15 grind setting on the MDF works best. Most might consider the resulting grind to be too fine for drip coffee; but I feel I get a nice, rich, full-bodied extraction out of my drip coffeemaker with this grind setting.
In a nutshell, the best grind is going to be whatever suites your palate; so practice, taste test, and enjoy! Do you have a Gaggia MDF at home? If you do, share your favorite grind settings with us.