I like that it can convert emails from multiple accounts at once so you don't have go through each account separately when doing mass conversions or just plain sending out large quantities of email messages! It is not as easy for new users but they do make tutorials available online which allows someone with no programming experience some assistance in using this program easily enough without having too much trouble learning how everything works together.
There are many other programs more user friendly than total mail converter pro such has Thunderbird's built-in message composer; however if all your looking for is simply converting mails between different formats then there isn’t anything wrong here really - unless maybe cost effectiveness?