Had quite a few of the steel shelves buckle, they are not really rated to hold 200kg of paper which is what they were loaded with, files that got consolidated into archive binders and they were added to till the whole shelf space was solid paper.
Also do not like being used as a ladder to reach the top shelf, though if you stack 2 shelf units right on each other so the lower adds extra support it does well, and those little corner diagonals are not going to hold up under a 300kg load, you need the solid sheet backing or side braces instead. Otherwise they will handle a load up to the point where the leg ends punch through the vinyl floor tiling from the load.
Got quite a lot of it though, must put some together if I need more storage space.