My thoughts after having used PB5 for the past month: It's a small incremental improvement over PB4. And now that 5.0.10 was released, I'm not having as many bugs as I did.
I've grown to like some of the features, such as emoji support, color icons, message filters that go across all accounts, and the message size indicator.
(For example, sometimes I'll hit reply and see that my reply is 5 MB and it reminds me to go delete the embedded image that was in the message I'm replying to… some people embed images like that instead of attaching thing.)
Anyway, I'm back to being generally pleased with Postbox. But I'm also annoyed that they're going backward in other ways… the fact that Config Editor is now blank unless you know what to type is really frustrating.
And I'm frustrated that they don't seem to be adding significant new mail organization features. For example, "Favorite Contacts" is great but if one contact has 3 or 4 different email addresses they email from, there's no way to group them. The Advanced Find dialog box works, but it takes far too many clicks and time to "dial in" what I'm looking for.
I hope they're reading this, and listening to their customers! :-)
--david b.