The biggest lack in product development is getting "blind" and not having enough resources.
Having the chance to work with outstanding UX/UI Design talent is a unique opportunity to evaluate your status quo from a hollistic perspective, but also to get a fresh view and new creative and most important non-biased input from professionals.
Reviewers will also try to give you a lot of examples and best practices to help you improve!
Not convinced? We have many more reasons ;)