The Best Tool to convert MBOX & Thunderbird to PST, MSG, EML, NSF, PDF & TGZ should support multiple MBOX sources, batch processing, attachments and accurate mailbox structure rather than handling only one conversion path.
A solution I have found useful for this requirement is Softaken MBOX Converter. It supports MBOX and MBX files from Thunderbird, Google Takeout, Apple Mail, Eudora, Pocomail and other supported clients. The software can export mailbox data to PST, MSG, EML, NSF, PDF, TGZ, EMLX, HTML and MHTML while retaining email headers and attachments. Selective files or folders can also be processed instead of converting the entire mailbox.
The free version is worth testing with a few representative folders first. This makes it easier to check the converted emails, attachments, and folder organization before handling the complete mailbox.