The Knipex Plier Wrench has jaws close parallel and apply pressure to to the hex or square flats on the nut or bolt you're trying to turn. This is great for solid bolt or fitting heads, and fine if the nut you're turning is strong and sturdy, but if you try to use it on something like the chrome plated zinc nuts for P-traps under sinks, the Plier Wrench can apply enough pressure to distort the nut, and it actually can become more difficult to undo the plumbing, and there's a chance you can damage the fittings. In this case you're better of with a ford style adjustable monkey wrench, or a Crescent wrench, or one of the ridgid hex jaw pipe wrenches.
Between the German/Swedish design pipe wrenches and US Ridgid designs it probably depends. The German wrenches are more versatile, and in a pinch can be used like a set of pliers to hold shapes other than round pipe. You make also be able to keep aplying pressure to both handles and wiggle a fitting back and forth if necessary, although the wrench won't grip as well in one direction.You also have to keep hold of both wrench handles so in awkward situations the could make things a bit more awkward.
With the ridgid type wrench, you just adjust the jaw opening with the nut, and make sure to put the wrench on the fitting to turn it in the wright direction. If you want to turn the wrench in the opposite direction you have to remove the wrench and regrip the fitting from the opposite side. the Ridgid pipe wrench design is just simple and solid, and once you adjust the jaw opening there's little to **** about with.