When choosing an outdoor auto open three-folding umbrella, here are some factors to consider:

1. Size and Coverage: Consider the size of the umbrella when opened and its coverage area. You want an umbrella that provides sufficient coverage to protect you from rain or sun. The diameter of the opened umbrella canopy should be large enough to keep you comfortably dry or shaded.

2. Durability and Construction: Look for an umbrella with a sturdy and durable construction. Check the materials used for the canopy, frame, and ribs. Canopies made of polyester or nylon tend to be more durable and water-resistant. The frame should be made of strong materials such as fiberglass or aluminum to withstand wind and maintain its shape.

3. Auto Open Mechanism: Ensure that the umbrella has an automatic open feature. This allows for quick and easy opening with the push of a button. Test the auto open mechanism to ensure it operates smoothly and reliably.
   

4. Folding Design and Portability: Consider the folding design of the umbrella. It should be compact and easy to fold down when not in use, making it convenient to carry and store. Look for a lightweight umbrella that won't be a burden to carry around.

5. Wind Resistance: Check if the umbrella is designed to withstand wind. Look for features like a vented canopy or a double canopy design, which allow wind to pass through without turning the umbrella inside out. Reinforced ribs or a strong frame construction can also enhance wind resistance.

6. Handle and Grip: Pay attention to the handle of the umbrella. It should be comfortable to hold and provide a secure grip, even when wet. Consider features like a non-slip or rubberized handle for better control.

7. UV Protection: If you intend to use the umbrella for sun protection, check if it offers UV protection. Look for umbrellas with a UPF (Ultraviolet Protection Factor) rating, which indicates the level of protection against harmful UV rays.

8. Water Resistance: Ensure that the umbrella has a water-resistant canopy to keep you dry during rain showers. Look for umbrellas with a water-repellent coating or a canopy material that naturally repels water.

9. Style and Design: Choose an umbrella that suits your personal style and preferences. There are various designs, colors, and patterns available, allowing you to find one that matches your taste and complements your outdoor attire.

Remember to consider the specific features and requirements you prioritize in an outdoor umbrella. Whether it's durability, wind resistance, portability, or UV protection, finding a balance between these factors will help you select the right outdoor auto open three-folding umbrella for your needs.