As one who has never used GitLab, I'm uncertain about the changes.
To educate me can anyone point to an instance of a merge commit in another project?
If I understand them correctly (which might not be true) then I'm a -2 for merge commits. I really do NOT want to see master commit history polluted with the details of the sausage making, just the effective change.
To clarify discussion on this I would like to see detailed workflows of both approaches (ff only and merge commits), i.e. intial change creation, amendment, approval and merge to master, along with any tooling (e.g. similar to git-review) that makes the process easier.
When we have the workflows laid out then we then have a basis for discussion as to which fits the project needs better.