Yes, I am a switcher. It's been many years, but I still have some old emails in .msg format from the bad ol' Windows days. Previously I was using TextWrangler to read the text portions of the emails, but it wasn't an ideal solution as there is a lot of other stuff in there in addition to the text, and if there's an attachment, too, then it gets really ugly. MailRaider is a great alternative. It displays the emails without any unnecessary clutter, saves them in rtf format, and provides easy access to any attachments.
The only downside I can find is that all of my emails show up without a date and time, presumably because they have been saved as individual .msg files and not in an Outlook database or something. Fortunately, I always set the date and time of the .msg files to match the email, so I know the correct date and time.