1. Validation: Formstack provides pre-built validation rules and customizable validation messages for form fields, while React Hook Form allows for custom validation rules and error messages that can be easily implemented based on specific requirements.

2. State Management: Formstack manages form state internally, simplifying the process for users, whereas React Hook Form provides more control over managing form state by allowing developers to store and manipulate form data in the React component itself.

3. Performance: Formstack may have limitations in terms of customization options and performance optimizations compared to React Hook Form, which is highly flexible and efficient for handling complex forms with minimal performance impact.

4. Community Support: React Hook Form has a large and active community of developers contributing to its ongoing development and maintenance, while Formstack may have a more limited support network and resources available for troubleshooting issues and finding solutions.

5. Integration: Formstack offers seamless integration with various third-party tools and services, simplifying the integration process for users, while React Hook Form may require more manual implementation and configuration for integrating with external platforms.

6. Learning Curve: React Hook Form requires a certain level of proficiency in React to utilize effectively, making it more suitable for developers familiar with the React ecosystem, while Formstack offers a more user-friendly interface that is accessible to users with varying levels of technical expertise.

In Summary, Formstack is a user-friendly form solution with pre-built validation and state management, while React Hook Form offers more flexibility and performance optimization options for developers familiar with React.