I quickly filled up my 5 tier shelving units with office supplies, tools and printers. If I would have known sooner, I would have connected them to end up just one piece. So they wouldn't wobble. But trust me, they are very hefty and can hold stuff.
As you can see my 5 tier shelving unit from Walmart, holds plenty of my stuff. 7 printers, two YourStory book binding laminating machine, 6 hot pink stackable storage boxes, and whole lots of stuff. It was a good decision to get these low budget shelving unit from Walmart.
I added a small one drawer desk in front of my bookshelves for easy access to the printers, I often uses.