Maru 4x4's have these little bumps on the inside and until you wear them down, they don't perform as well as people with used ones say. So you can either sand down said bumps or just use the cube.
Maru 4x4 have 2 rivets (Yes, even though they look like screws) which cause that "bad side". The best solution is just to work it in more and it will eventually get better.