What are the ways to import large MBOX files into Thunderbird?

Hi all,
Importing large MBOX files into Thunderbird has been a challenge for me. Manual methods often fail or take too long, so I tried a third party tool. It performed really well, handling large files smoothly and without data loss. While I’m impressed with the tool, I’d like to know if there are other effective solutions or alternative tools for this task. Has anyone come across methods that are equally efficient or even better?