At 59, it's 9 days of two trips to recoup the cost -- still very worth it for someone living in Germany, but a bit more borderline for a tourist.
Compare with eg Toronto's monthly pass, which is $156. A single trip is $3.35, which comes out to 24 two-trip days to recoup the cost of the card. That's almost exactly the number of business days in a month. And that card's only for Toronto!