> On one hand, a more efficient fridge would cost less money on the long run, but on the other hand i'm afraid to buy a lemon. So I'm patiently waiting for my Siemens to die

There's a piece of wisdom about cars and appliances that unless there's some egregious defect that turns it into infinite money sink, the least costly (and in fact the most environmentally friendly) option is to run the one you currently have until it disintegrates. Because the price of a new one is usually like your electrical bill for the current one over multiple years, adjusted for inflation and price hikes.

There are of course exceptions, but rules of thumb are never 100%.