Internal HR or the Manager would already have an opinion on the employee (Predetermined mindset) which will not help them on understanding the employee's needs and expectation. An unknown person can crack the real issue as they don't know each other's background.

Obviously, there are metrics through which the employee will be interrogated and required information is received. 3rd party assessor can bring in more surprise to the organization

Obviously, the solutions are with the CEO and the HR. But it will be difficult for them to identify the roots of the problem. What seems to the issue for the internal people and 3rd party assessor will be totally different.

Employers can make use of the 3rd party employee satisfaction audit services to retain the best talents in their organization.

This process could also be used for determining the employee engagement, process implementation, process documentation for quality standards & as well as an external Chief Human Resource Officer.