[rmaccloy]

They're not mutually exclusive: you want basic correctness/design review of course (my favored approach is now pre-integration code review + authoritative master/master-always-deployable), but a proper feature-flagging system will let you beta or A/B test potentially incorrect (in a code-correctness, performance, or UX sense) changes gradually in the real world. Binary (on/off for everybody) flags are more the exception than the rule.

Server affinity + staged rollouts are another approach, but for long timeframes (e.g. A/B UX tests, feature prototypes) I'd think you'd want to go with flagging anyway from a codebase management point of view.

Some things do take more effort to make dynamically flaggable than it would take cost to delay integration, to be fair. Judgement call.