I would not hesitate to use those as you plan. Those shelves are very strong, and the design is often used in industrial applications. They look to be 24" deep, so you'll have some wasted space with 12" deep 20 Longs.
I'll add though, that while I would not hesitate to use them, if I were making the setup I would build from scratch with 2X4s and have exactly what I wanted for a very small fraction of what those cost. Seriously though, you could buy a Skilsaw, Estwing Hammer, and all the materials for one shelf and still beat that price. And when you're done you still have the Skilsaw and hammer!