Someone neatly wrote up the main advantages:
http://cramer.io/2014/05/03/on-pull-requests
Phabricator's issue tracker is also an excellent choice over GitHub's simplistic issue tracker.
Also, Gerrit isn't that hard and I've seen small teams get productive with it within a 1-2 weeks.
No need to reinvent the wheel!
By the way: I live in Europe and I haven't worked for one single company which would allow their developers to host proprietary source code with a third party SaaS provider.
> By the way: I live in Europe and I haven't worked for one single company which would allow their developers to host proprietary source code with a third party SaaS provider.
Fair enough, companies vary widely in their acceptance of SaaS -- though Reviewable has plenty of European customers too. But to clarify, neither Review Ninja nor Reviewable (not sure about Omniref) actually host code themselves: they just access it through GitHub APIs without storing it. You can also deploy Review Ninja (and soon Reviewable) on-premises, though of course that means you're on the hook for administrating the system again.
That's the nice thing about Phabricator, you can switch off all features you don't need, and it integrates with GitHub. You can definitely use it just for code reviews, with users logging in using their GitHub accounts and the repositories being hosted by GitHub.
> You can also deploy Review Ninja (and soon Reviewable) on-premises, though of course that means you're on the hook for administrating the system again.
That would work! Third party SaaS probably includes Github.
A lighter-weight SaaS like https://review.ninja, https://omniref.com, or https://reviewable.io (disclosure: this one's mine) might be a more appropriate solution. Specifically to the article's points, Reviewable has a nice reviews dashboard and will show inter-commit diffs within a PR (whether you're rebasing/amending or not), hiding any files with no changes since you last looked. Its default review completion criterion is that all files have been marked as reviewed by at least one person and there are no unresolved discussions still going on, but you can customize this to your team by writing a snippet of code to run against the review's state, e.g. to implement LGTM approval or even a voting system. Reviewable will also update a status check on the PR so you can enforce review completion before merging if that works best for your situation.
Best of all, because both systems integrate tightly with GitHub, there's no need to learn a new workflow or mess around with new git commands. Gerrit still has its place but I don't think it should be the tool of first resort.
(Edit: added mention of Omniref.)