[dominotw]

I am not too familar with gitlab. But I am assuming that button click triggers another build ?

So its not just 'one button rebase operation' its 'one button rebase and wait for build to finish operation' before it can be reviewed again.

[chusk3]

Yes, that's the case. However there's also the 'merge this when the build successfully completes' that means you can push one button and walk away. They are also developing features around MRs that 'ripple' in this way, so that when you have several going the rest will continue rebasing+building until they either fail the build (due to changes that are no longer correct), can't be rebased (due to a need for conflict resolution), or finally merge successfully.