Well, I'm using 3 POP3 accounts and 2 IMAP accounts. Having them in one application is much more comfortable for me than regularly checking each in the browser. Plus Thunderbird's filtering and organizing capabilities and its spam filter. I've been using it with the maildir file format for years, and it has been absolutely stable for me although my profile folder is about 6.1 GiB large. But each to one's own. If the "feel" is not the right for you another theme might relieve your dislike.