This is included in the “About” section of Shift. So take it as you will...

Depends on your needs. Outlook doesn’t offer the Gmail web interface, doesn’t sync with Google Calendar, and doesn’t integrate with Drive or the Google Apps suite. As I mentioned in an earlier reply though, I’ve been using a different app for this that doesn’t require a subscription.

Great recommendation, just set it up as I have a corporate Gmail account and personal and the free plan fits perfect for me.