In the U.S., where I live, Master’s Degrees in graphic design aren’t especially common. I don’t know if the same is true in Italy. I went through my MFA program in graphic design about 20 years ago, so I’ll answer your questions from those perspectives.
Few companies here specifically require Master’s Degrees for graphic design. Having one, might even make those first entry-level jobs a little more difficult since a person with a graduate degree might be seen as overqualified and underexperienced.
I haven’t found my MFA to be especially useful, nor did I find the academic courses associated with it to be either practical or useful except from an academic point of view. It has, however, opened a few doors for me to more advanced positions in the field. I wouldn’t be at all surprised to see Master’s Degrees in design becoming more popular in the future as designers begin to seek out additional ways to make themselves stand out and appear to be more qualified to employers in what has become an oversaturated field.
Your situation is different from mine, though. Both my undergraduate and graduate degrees are in graphic design. You seem to be pursuing a Bachelor’s Degree in Product Design and wondering if a Master’s Degree would be a good compliment to your Product Design degree. I think those would be a much more useful combination of degrees than the ones I have.
Let me explain:
The combination of two different, but related kinds of degrees broadens your appeal to those companies that could use the skills that come from both. For example if you applied for a position at a company built around developing and marketing new products, I can see a degree in both product design and graphic design being complimentary to each other and seeming very valuable to the employer. It might also serve you very well in future promotions within that company.
On the other hand, those two degrees will have a tendency to make your education very specialized in the sense that not every company needs both a product designer and graphic designer.
Another potential problem is that all those years in school will not give you the practical experience needed to get those first entry-level jobs. It’s sometimes quite difficult to make the adjustment from academia to the real world, and those extra years of schooling can make that adjustment even more difficult unless the student makes a point of actually working as a designer (internships, part-time, etc.) while going to school or, perhaps, taking a year or two off and working professionally between the two degrees.