It depends on your specific use case. Here's a breakdown to help you decide: 


Scenario
Recommended Option
Why
You want to download and upload files within the same Salesforce org
Buy MFD + MFU apps
MFD handles downloads, and MFU handles uploads. One-time license fee for each. Ideal for ongoing, internal org usage.
You want to migrate files from one Salesforce org to another
Buy the MFM app only
MFM supports both direct migration, so no need to download and then upload the files.  You only pay for the actual data migrated via credits, cost-effective for cross-org migration.