When you go to roll the Kallax on it’s casters, push near the bottom of it’s side, rather than the middle, or even worse, near it’s top. Perhaps because it has no back panel, the Kallax exhibits some "give" in the lateral direction. I pushed on the top corner at one end of both the 16-cubicle and 25-cubicle Kallax, and they weren’t completely stiff---the whole assembly became out of square. I did the same with the 4-cubicle Eket, and the box remained square, showing no sign of movement. Now that I have assembled my Ekets, I can attest to their structural strength and stiffness.
There have been reports of the larger (16 and 25 cube) Kallaxs collapsing when fully loaded with LP’s. When I was going to go with them, I was intending to get multiples of the 8-cubicle version, as many as necessary to hold all my LPs. I would lay the Kallax on it’s side---horizontally as Davey intends, rather than place it vertically, standing up. Adding a cross-member to the back of the Kallax, as some have done, is also an idea worth considering. The Kallax is definitely the best value around, the cost per LP very low. Just be gentle with them once they’re loaded!
By the way, the "beefiness" of the Kallax, if it is perceived that way because of the thickness of it’s outer panels, is illusionary. Those panels are made of lightweight pressed-fibreboard, that "hollow-core" stuff, as are those of the Eket. The Kallax’s thicker outer panels, in comparison the those of the Eket, provide no additional strength.