Southwestern shades may be hard-back or soft-back. Each has its own pros and cons.
The hard-back Southwestern lamp shade has the purpose of maximizing the light output towards the top and bottom. To achieve this, light coming out to the sides are blocked and re-directed. It's the reason why hard-back typically comes with a dark color on the outside and a shiny metal sheet on the inside to direct the light. Because it maximizes the light downwards, it's a good option if you need a lamp that provides illumination while doing something at a desk or table.
The soft-back allows the light to pass through the sides. Thus, such kind of shade comes with a sort of fabric cover. Since the light is not overly focused, the light output is more diffused. It's the reason why a soft-back lamp shade is a great solution if you are in need of ambient lighting.
The trick to avoiding costly mistakes when purchasing a Southwestern lamp shade is knowing how to narrow down your choices. The points mentioned above should help you filter your selections into a more manageable list. If you are still left with too many options, feel free to add more filters like the style, size, and costs.