I bought the external filter for my 20l Nano-Cube and lo and behold, the filter came the very next day with me healing and well packed in! The filter is very easy to use and with only 3 watts power consumption and also economical. When I washed the filter materials, I noticed that the activated carbon was very dirty (possibly by transport). The only downside is that the manual is not in German, but my beautiful pictures!
Conclusion: The filter is geeigent for aquariums up to 60l and highly recommended!