Pros
Above all - In general H&M is a nice company. The culture, corporate behavior is refreshing and young. The Management (Store Manager/Dept. Manager) are used to have a cooperative leading style. If you're showing up with certain motivation there are great chances to grow and get experienced as well in parts of visual merchandising. Beside that you'll get staff discount and other benefits while working at the H&M group. The colleagues are in general young/remained young. It's never getting boring since you are always busy there - also the time is running.
Cons
Many times there are just not enough employees available and it's getting crazy busy. Lot's of time pressure. As a job beside studying - completely fine. Otherwise with the flexible working hours contract it's almost not possible to plan/have any free time - since you may have to step in just for the next day. (I mean as long as you have to rely on the money of this job) Pretty Exhausting