What this does, and what it doesn't
HumanFlow rewrites text so it reads naturally — varied sentence length, plainer verbs, fewer of the constructions that make a draft sound machine-made. It does not promise to beat any particular detector, because nobody can honestly promise that. Detectors disagree with each other and flag human writing too.
Use it on your own drafts, and read the result before you send it. If a score matters to you, read what detector accuracy actually means first.