Useful as a research participation incentive
We have used these successfully as research participation incentives when recruiting online research participants. They arrived fast, were well packaged, and worked as expected. One issue is that some people, particularly people from specific subpopulations, object to Amazon's reportedly unethical treatment of employees and contractors. This may discourage potential research participants from housing the research. Other gift card recipients may similarly have an issue with Amazon’s practices and decline to use the cards.