DO NOT BUY
This puzzle is really interesting conceptually and I thought that would be enough to make up for sub-par turning so I bought the puzzle. Unfortunately, this is the most poorly made puzzle I have ever had the misfortune of using.

When it is scrambled at all, the pieces become extremely loose and wiggle around. This causes extreme misalignments and truly CONSTANT lockups that can take minutes to fix. I have also had edge pieces pop out and corner pieces rotate themselves in-place. I have tried adjusting the tension and anything else I could think of and it made 0 difference.

Stay away.

Do not buy.
One important criteria of a cube is that it can turn. This one locks up because the lengths of each edge and corner are not consistent. This means that to turn a side, you have to angle it so that it will cut corners--"cutting corners" being necessary since it doesn't turn properly.
It uses the same mechanics as a 3x3x3. The edges and corners cross the same way a 3x3 does, meaning you can use most of the same algorithms, it just takes longer. It is similar to a hexaminx.
But because it doesn't turn well, it takes hours to solve. I can solve a 3x3 in a minute and a 7x7 in ten. This took so long because you have to squeeze pieces together in order to get pieces to slide past each other. The jumbling is a mess and the pieces can actually get caught on each other on the outside of the mechanism as well as on the inside.
Very poorly constructed. Does not work as a functioning puzzle.
It also breaks easily. The plastic is cheap. The centers are snapped on with two pieces, one outside the core and one inside the core. If it snaps off, the one inside the core will fall inside and will bounce around the center like a ball inside a sleigh bell. Impossible to fix. With only one break, it is still somewhat workable, but it falls apart easily after that.
If it were $7, it might be worth it just because it is cool to look at and helps complete a collection. Not worth your money. It is not fun. You will become frustrated not because it's difficult, but because it's so hard to turn a side.