UltraSearch allows you to access to your SharePoint directly without having to create your own Azure AD registry. This option is user-friendly and is aimed at users who want a simple and fast connection.
Please note that when you first login, UltraSearch will ask you for permission to perform searches on SharePoint. In some cases this will require the approval of your administrator. This approval should be tenant-wide and is only required once per company/tenant.
For granting tenant-wide consent without having to install UltraSearch first, this link can be used.
Alternatively, you have the option of using your own Azure registration. This option offers you extended control and flexibility if you want to control or further restrict access to your SharePoint for users or use certificate-based authentication.
You can find out how to configure your own Azure AD registration here.