Well, I wanted to love this app, it seemed really promising, but my trial is not really convincing...
At first, I thought "Great!" when it offered to import accounts definitions from Mail or Postbox, but it didn't work well: I had to manually edit each of my 12 accounts, add the user name and check port 993 (SSL) — it didn't seem to matter whether I put my pw at this stage or not, it would ask it again (or not!) when syncing.
Sometimes "Edit account" (menu or right-click) was not responding at first try...
Once done, I had to sync the account for something to happen, it might ask once more the pw, as mentioned earlier, but in any way, it only worked if "Save in keychain" was unchecked!!! Sometimes I had to do it a few times before it works.
All this was totally impossible for Gmail: it sends me to my default browser and once accepted by Gmail, I have once more the message to send me to my default browser... (tried many times with clean profiles in Chromium, Firefox or Safari)
After relaunching the app, I had of course to reenter each pw (SBBOD when checking "Save in keychain"...) — this only will be a showstopper, for me!
Once done, the app seemed to work quite ok except I had to do it twice or more when deleting mails...
I'm giving 2 stars because I'm a good guy ;-) but it certainly doesn't suits my configuration (it might work better in recent OSes, I'm still on OS 10.9)