Are no-pull front-clip harnesses actually effective?

Across specialist subreddits like r/Dogtraining and r/dogs, the consensus is that front-clip harnesses meaningfully reduce pulling by redirecting a dog's forward momentum, and several owners describe near-immediate improvement. Reviewers caution that they are a management and training aid, not a cure, and that some front straps can slip out of position on deep-chested dogs unless fitted carefully.