Why should you use the SFDMU?
Creating of a scratch org, dev org or even a sandbox today is a pretty fast and simple action. On the other hand the newly created organization has only metadata ready-to-use, has no real data that is always strongly required to develop and debug any Salesforce application. It makes no sense to manually create or load data traditional way (with the Salesforce Data Loader) for each new org because the data easily can be taken in whole or in part from production or from the sandbox and imported into the new organization.
In some cases we already have the data, but it's only required to modify particular records or even fields without touching others. When a date model is complex and contains a large number of dependencies, it becomes a very hard and annoying task.
Also there is a situation when as client you would like to keep the data model clean without creating external ID fields in the SObject, therefore your goal is to find some workaround to update records in your developer org from the existing source without adding new fields.
Population of the RecordtypeId field is another quite difficult task, when ids are not consistent between environment.
At current moment, there is no effective tool for both inserting and updating dependent objects based on any unique field used as External Id. In most cases people use Excel spreadsheets to build source tables and try to mix between them to get proper values for the lookup or master-detail fields. So filling out even a small number of objects turns into a huge pain...
Why the SFDMU Plugin is the best solution?
It provides the most convenient way to export data from multiple related sObjects between Salesforce orgs (even unlinked). Unlike other similar tools it can easily and quickly perform all important operations like: INSERT / UPDATE / UPSERT / DELETE.
Implemented a huge amount of advanced features never were before in any of the existing tools, which make your data migration very quick and easy.