The cubic 3x3x9 is a natural addition to the cubic 3x3xn family. Like its baby brothers and sisters, it remains in a cube shape when you scramble it. It's made by Witeden and comes in several versions. This one is like the 3x3x7 but with the equator slice split into 3 as well as the other layers.
Solving this is like solving puzzles within puzzles. I prefer to straighten out all the thin layers before doing anything on the cubic puzzles. After this, pieces can only be in the correct layer or the opposite one. The very middle layer of the puzzle (equator when the puzzle is as shown in the image) is easily solvable when all of the other pieces are in place. You occasionally have to swap some identical pieces to be able to place the middle layer but this isn't hard to do on the cubic puzzles.