First, except for the rubbery plastic layer where your feet rest and the bottom four corners with semi-rough rubbery plastic that sit on the floor, the 22 inch wide 3M Foot Rest is made of thin but totally adequate steel sheet metal.
I write "totally adequate" for use as a foot rest under a desk or table: If someone decided that they wanted to "rock and roll" on top of it, then it might break down after a while.
The "rock and roll" comes to mind because I didn't realize that the foot rest would pivot it you moved your feet above the center where the bolt-rubbery-washer-frame-steel-washer-lock-nut combo holds the top to the bottom frame, and applied some small amount of pressure, with the opposite effect when you move your feet back towards you and apply any pressure downward.
The pivot adds an unexpected and nice addition of flexible movement for your feet, ankles, and lower legs.
One will need some tools to assemble this.
The bottom frame can adjust the foot rest platform up and down in terms of height and angle. There are a few or at least two variations on that adjustment. Be prepared to wear some work gloves or heavy rubber gloves when assembling or adjusting the bottom frame: The inner hardware is a large wing nut, while the outer head of the bolt is a flat thumb screw. I wound up using an (adjustable) crescent wrench to grip the thumb screw head steady, while my rubberized work gloves tightened the wing nuts.
Between the materials used, the "just right" tension on the pivoting, and the additional width that this foot rest offers over the others makes it a perfect fit for me: I'm 5'9", so I suggest that anyone taller will definitely need the extra width that this model has over the others, which as I recall varied somewhere around 18".
I don't recall "exactly" what I had to adjust or assemble in terms of the "pivoting" assembly. The inside lock-nut is 7/16" I think, but the outer bolt head of that assembly may be metric, because none of my less that 1/2" box or open end wrenches would fit it, so, again, my crescent wrench came in handy.
I am at my desk/computer for many hours a day and finally succumbed to "reality" and purchased and Aeron chair, which I also recommend. However, the Aeron still made my stationary hours feel like something else was needed (aside from getting up), and for me, this foot rest seems to be the perfect complement to my "stationary hours."