A specialized tool (Etchmate, Hold-n-Fold, RB, etc) is not as important as is an understanding of the sequence of bends you will need to accomplish in order to make a 3D object out of a 2D sheet of metal.
In my opinion, the best way to learn that is to use a pair of opposed single-edge razor or scraper blades. (Its also cheaper.) Place one on the top of the part at the fold line as the hold down. The other is slid under to face the opposite blade. The bend is made by raising the under blade in a hinging motion. Flat-jaw pliers can also be used but they have a smaller jaw surface than does the razor blades. Bends made with pliers are more prone to twists.
Once you get the hang of the process, then get the tool and transfer the knowledge to how it works. Just having the tool in your toobox won't make you any better. You will need to practice to be able to repeatedly perform the necessary actions.
Me, I sat with the inventor of the Hold-n-Fold at an IPMS Nats a few years ago (damn, it must be near a decade now) and he taught me how to use it. A couple of years later I even worked hist stand while he toured the model room. I saw how it was easier to transfer the knowledge I had picked up "on the street' to the use of the tool. I have a H-n-F 4-inch and a H-n-F 2-inch. They suit my needs. Unless you build armor with needs for long folds on shurtzen skirts you probably wouldn't need anything larger than the 4, a good all around tool.