I've tried that too and agree that it has a slick UI. However one inconvenient design choice is that it stores all the messages (headers and bodies) in a giant

I've tried that too and agree that it has a slick UI. However one inconvenient design choice is that it stores all the messages (headers and bodies) in a giant sqlite database. Sure, full text searches and Gmail-style multiple labels per message are easy to implement this way, but a multi-GB single-file database is harder to back up efficiently and might be less robust than a maildir-type backend, which other clients such as Evolution use.