Why is bucketing users the better approach? To me it seems like bucketing would ignore "all other factors" that also changed, whereas dynamic (or periodic) switching seems like it would normalize those "other factors" across both A/B (ideally).
I'm not sure I totally understand why, because if a user follows you after seeing the other profile version, it might be because he preferred this other version.
But conceptually it makes sense to eliminate as many variables as you can to isolate the components of the test.