A "knock off" by definition is an unlicensed copy of something, esp. fashion clothing, intended to be sold at a lower price than the original.
The Devi Kroell bags are NOT unlicensed copies. Therefore, they're not knock-offs.
It's basically how designers have multiple levels of their line. For example, Ralph Lauren does his Collection line, Ralph Lauren Black, Ralph Lauren Blue, Ralph Lauren Purple, Ralph Lauren, Lauren, Lauren Jeans, RLX, Ralph Lauren Golf, Ralph Lauren Tennis, Polo Ralph Lauren, etc.
This is just another way for a designer to get his/her line "out" there for the public and to generate interest in his/her work. If you love the item, who cares how much it costs?