what actually works to clean rust off cast iron?

both guides are probably right, they're just for different amounts of rust. light orange haze: scrub with coarse salt and a splash of oil, wipe, re-season. proper flaky rust: soak in 50/50 white vinegar and water, check every half hour, and pull it the moment the rust lifts because the vinegar keeps eating the iron after the rust is gone. scrub with steel wool, dry it on the hob straight away, thin coat of oil, bake upside down at about 230c for an hour. the mistake people make is leaving it in the vinegar overnight.