Yeah, Outlook is great but it has some weaknesses. In particular, it's pretty bad at actually doing email. Message quoting is something that is basically broken in Outlook. You can't use HTML email at all, it must be plain text, and even then it has massive issues. Numerous people have complained about terrible message formatting when sent this way. No issues in MailNews. Here's an example from O2K7: https://w2k.phreaknet.org/o2k7/
I use Outlook for calendar and contacts, sometimes reading, almost never for composing or replying to email, unless it's the Exchange account which I use mostly for calendaring/contacts these days and "read only" email.
TB/derivatives have turned out to be much better at supporting the email standards, so MailNews just works better. Initially it was annoying to have both open all the time, but I've kind of gotten used to it; sometimes I'll close Outlook after the workday is over and there's nothing left on my calendar for the day.
On the other hand, Outlook obviously does Exchange, which TB doesn't. Effectively, both programs are required so I've just made peace with that.
Yup, exactly! I tried TB itself out and had some bad experiences with it, though that might have been XP + TB and not TB itself. But it sort of went the way that FF did, so MailNews has been much nicer.
At one point on this site I think I found an unofficial installer script for the Roytam programs. Problem was it didn't quite work right, since it assumed UAC would always be disabled and only admin users would ever use it, plus it didn't work cross-NT platforms. I added some patches so it works as a proper installer now - works from W2K through W10, and installs programs for all users (technically portably still, but in the Program Files directory) and adds desktop and start menu shortcuts in the appropriate places. Just used it to put New Moon on W2K.
If the program is already installed, the installer just overwrites the files, so if the batch script were a startup script via GPO, the roytam programs would all get updated automatically on reboot. I haven't done this, though; I just manually update once in a while. In the future I think it would be nice to mirror the repository locally so if I did this update mechanism it would pull locally, not over the Internet.