In order to use the app you are required to setup an account with Atlassian. This will set you up with an account with Bitbucket - and getting you signed up to Bitbucket is undoubtedly the main reason for Atlassian to make this app free. Offering a meagre 1Gb of storage, Bitbucket is among the most expensive git repository hosts around, and therefore has never enjoyed wide adoption among small developers. Its arch-nemesis is GitLab: a service that offers unlimited, free private repositories to all - with just about every feature available in Bitbucket, and then some.
But once you get through your Bitbucket registration, you will be greeted by an interface which looks very much like a java app that has received some polish. The 'native' feel of a MacOS app is certainly not there, windows look odd, navigation is clumsy and unintuitive.
But worse still: the app will only help you automatically connect to accounts in Bitbucket or GitHub - no GitLab, nor any of its other competitors. I'm guessing it may be possible to connect to these other services (just as you can connect to GitLab repos from GitHub's own desktop app), but that is certainly not the way the app was meant to be used.
All in all: pass. Straight to the trash, and back to using Tower, until I find a reasonable substitute that won't charge me a subscription fee.