The Fadi Cube (4x4x4) is a higher-order variant of the Redi Cube. It was invented in 2009 by Oskar van Deventer. It was mass produced by Meffert's between 2010 and 2012 under the name Mosaic Cube, and by LanLan since 2018. It is interesting to note that the Fadi/Mosaic Cube actually started being mass produced 7 full years(!) earlier than its younger sibling, the Redi Cube. On their website, Meffert's write about going through 5 different prototypes before releasing it as a collectors puzzle (not meant for speed solving). It is believed Meffert's were never fully satisfied with the design and the clunky turns, which eventually led them to pull the plug on production all together.
Much like the Redi Cube, the Fadi Cube turns around its corners, and in the same way that the Redi Cube is a Dino Cube with corner pieces, the Fadi Cube can be thought of a Lattice Cube with corner pieces. The Fadi Cube is obviously harder to solve than the Redi Cube, however, it is not considered to be very hard to solve. A common approach to solving the Fadi/Mosaic Cube is by reduction: To begin, pair every 2 adjacent edge pieces with their respective center piece, then solve as a regular Redi Cube (3x3x3). In the early days, solving this puzzle as a Redi Cube was especially interesting since the Redi Cube itself didn't exist yet.
The Fadi/Mosaic Cube is not an official WCA puzzle. The world record for fastest solve is 40.92 seconds, set by Aedan Bryant from the United States.