The lesser key just gives you the demons and what they do.
The greater key tells you how to make them show up. And more importantly, how to protect yourself from them.
Not all the diagrams and floor drawings are required. And you can make a triangle out of canvas or cardboard. But if you expect magic to work, you have to respect its context.
You can also use an athame in place of a full sized sword. But a metal implement is clutch. It helps to cut through etheric energy, in case things get out of hand.
Seriously though. Magic is far more effective, generally, when you put the time, effort, and work into it. You can eat ramen all the time. But you'll be healthier if you cook a balanced meal. Magick is no different.