When choosing a useful pen, you can refer to the following aspects:

1. Pen tip material: The pen tip of a pen is usually made of stainless steel, gold, titanium alloy and other materials. Stainless steel nibs are wear-resistant and affordable, suitable for daily writing; gold and titanium alloy nibs are of higher quality, but the price is correspondingly higher, and are suitable for collection or gift giving.

2. Pen body design: The pen body of the pen is usually made of plastic, metal or other materials. Consider grip, weight and comfort when choosing. Some pens have ergonomic designs that are better suited for long periods of writing.

3. Pen tip width: Pen tip width will affect the writing effect. Generally speaking, wider nibs are better for signing and drawing, while narrower nibs are better for everyday writing.

4. Pen and ink capacity: Ink capacity is an important factor in measuring the cost of pen use. Large-capacity pens can provide a longer writing experience, but also make it more difficult to carry and clean. Choose the appropriate ink capacity based on your personal needs.

5. Brand and price: When buying pens, you can consider well-known brands, such as Montblanc, Pelikan, Parker, etc. The quality of the pens of these brands is usually guaranteed, but the prices are also relatively high. If your budget is limited, you can also look for some cost-effective domestic brands.

6. Trial writing: Try to try out the pen before purchasing to feel its writing effect, comfort and durability. At the same time, pay attention to check whether the pen tip is smooth and whether there is any ink leakage.

Finally, please choose the appropriate pen according to your needs and usage scenarios. No matter which pen you choose, you should pay attention to care and maintenance to extend its service life.