You would be hard pressed to find a single individual living on the surface of the earth who is not at the very least slightly familiar with business cards in some way, shape or form. The only possible exception to this rule that we can think of are uncontacted tribes such as the Sentinelese off the coast of India or one of the many tribes that have eschewed modern society and are instead living their traditional and ancient lifestyle deep within the Amazon rainforest at any given point in time.
The type of business card that most people would be familiar with is likely going to be rectangular in shape. This raises the question of whether your own Metal Kards need to correspond to these dimensions as well, or if you can use a different approach that may be a fair bit more innovative. It might surprise you to hear this, but suffice it to say that square business cards are quite common out here in the real world. A big part of the reason why that is the case has to do with the fact that they can be stacked more easily, and there is also the added advantage of them being more convenient to store.
Square business cards are still a new concept, and that gives you the chance to use them to great effect. Anyone that sees that you use square cards instead of rectangular ones would immediately recognize you as an individual that is innovative and willing to push boundaries. Rectangular cards are still useful, but they might soon fade away as square variants increase in prominence and quickly become the standard option for entrepreneurs.