This store is - compared to the american market - nothing special. It's quite big, they have a…read morevariety of different electronics but there's a huge downside. They don't really give you a choice. Saturn only carries a few brands in different pricing categories, so if you go there to buy a keyboard for your kid, you will only find Casio keyboards. The catch is, that Casio keyboards are utter crap, but you won't know because you don't see anything else. (Now you know!)
The pricing is decent, not cheap. You will always get better deals on the internet or even elsewhere in Hamburg.
The only thing I visit Saturn for (and that's why they get 5 stars to begin with) is the Apple Store. It's not really an Apple store, just a small part of the basement, but they hold every major Apple product. So if you need a new PSU for your Macbook because your dog decided that the Magsafe connector is really tasty, you can get it there.