First of all, accuracy is the most important consideration when choosing a free paper duplicate checking system. An accurate duplicate checking system can accurately identify plagiarism and repetition in papers. We can evaluate the accuracy of the system by looking at its algorithm and technical support. Some systems adopt advanced text matching algorithms, such as TF-IDF algorithm and SimHash algorithm, which can compare the similarity of papers more accurately. In addition, the technical team of the duplicate checking system is also an important reference for evaluating the accuracy, and their professional knowledge and experience will have an important impact on the performance of the system.

Secondly, privacy protection is also one of the factors that need to be considered when choosing a free paper duplicate checking system. Papers uploaded by users usually contain a lot of personal information and academic achievements, so the system needs a set of strict privacy protection measures to ensure the security and confidentiality of the papers. It is very important to understand the privacy policy and data usage of the system. We can choose systems that promise not to use users' papers and personal information for other commercial purposes.

In addition, user experience is also an important factor in choosing a free paper duplicate checking system. A good system should have a user-friendly interface and operation mode, so that users can upload and view test results conveniently. The detection speed of the system is also an important indicator of user experience, and users don't want to wait too long to get the results. Therefore, we can choose those systems that provide quick detection and friendly user interface.

Finally, the support of foreign languages is also a factor to be considered when choosing a free paper duplicate checking system. With the development of globalization, more and more students and researchers need to translate their papers into other languages for publication. Therefore, a good duplicate checking system should be supported by foreign languages and be able to identify similar content and plagiarism in different languages.