I wouldn't trust this to hold anywhere close to the rated weight, for that it gets one star. Like everyone says, the MDF bows under medium weight. Not only does it seem like it could snap, but it minimizes the contact area supporting the shelf. If you think cutting stronger material (plywood) to replace the shelves will fix the issue; it may, but these shelves are 23.2 x 47.2 you wont find a hardware store allowed to trim such little amounts off their plywood. Muscle Rack / Edsal has different quality of the same products, this as you could imagine by the price is the "overseas" version. If you want a detailed explanation on how to fix it - read on.
My first step was trying to reach Edsal. I called %26 called their support number no answer. So I submitted an online ticket. My primary goal was to get these cross or tie bars I saw mentioned in a Depot review. The CSR was very nice and shipped out 10 at no charge, but said they probably wont fit because the Depot version is different (2x price) than this "overseas" version. 1 star for their assistance. The bars came %26 like she thought, they were too long.
Another review I saw made their own cross bars out of wood. So I grabbed a cheap 2x2 furring strip %26 got to work. I mitered the edges (36º) to fit in with the steel angle. This worked great. In hind sight the review did 2 per shelf which I should have done, I only did one in the center. When loading down the shelf, each side still had a little deflection. It would probably hold, but I wanted to make absolute sure before filling up every shelf. I looked for stronger shelf material, but like I said I couldn't find anyone who would cut it to the exact size. I turned to the steel cross bars Edsal provided. With a little hammering, I could flatten one end and expand out the hook to fit right over my center bar. I did this for all 5 shelves (10 bars) and now everything is very sturdy.
It is important to follow the directions for shelf placement, I saw a review that had the bottom shelf way higher than the 3rd hole, this will 100% cause the legs to bend. This version doesn't include plastic ends for the metal feet. Go grab some flooring samples to stand it on, or it will cut through your carpet. I recommend anchoring it to the wall. I didn't have studs, so I used 4x 250%23 T style toggles. Make sure to use some sort of shim so its not pulling the shelf back. Also for a safety railing on the sides, Harbor Freight has 24" zip ties, which fit great if you use a pair.
After all that I have about 400%23 on each shelf and it feels very sturdy. In the end it may be worth just buying a nicer shelf, but the extra work wasn't that hard.