Best to go with air express
For the 20-unit challenge, we typically recommend having the units shipped by air. This is because air shipping is generally faster, usually taking about a week or two to get to you. While sea shipping might be cheaper, it can take significantly longer.
The goal of the 20-unit challenge is to get your product in hand as quickly as possible so you can start testing and validating your product idea. Therefore, the speed of air shipping is more beneficial in this case.
Remember, the cost of shipping for these 20 units can vary depending on the size and weight of your product. It could range from around 50 USD to 250 USD. If the shipping cost seems too high, don't hesitate to adjust the number of units in your challenge. The key is to get started without breaking the bank.