MaorThe Ahab is slightly bigger and uses a slightly different filling system, like a piston filling system, but you can remove it from the pen and convert the pen to an eyedropper filler (filling the body with ink) Whereas the Konrad is more like an up-jumped Creaper, it's larger than the Creaper, but it is also a piston-filled fountain pen. All can be stripped down to the constituent parts easily.
MaorFor the most part, just size. The Ahab is a bit bigger. The nib and feed are the same, but they fit in slightly differently into the grip section. They're both piston fillers, but the piston in the Ahab is a separate part inside of the body, and in the Konrad, the piston is integrated into the body like a TWSBI 580.