I used google translate and don't see a whole lot of comparison of degree of stealthiness in that article. It is a blog post of article from a defence magazine and there is no information on the author and his credentials wrt this topic. Meanwhile, a comparison between K130 and Milgem - whatever the outcome - doesn't inform the situation of Milgem v. Sigma (which, incidentally, is a range of different ships, not a single ship: SIGMA versions ranges from 500 to 2,400 tonnes displacement, while propulsion options range from twin-screw fixed or controllable pitch propeller, to twin water jets, powered by diesel engines, full electric drive, or gas turbines. Other options include signature management and NBC protection.) Kindly inform by what criteria you decide to classify a design as 'stealthy' and by what criteria as 'ordinary'.