It isn't actually bisulphate but it is the ingredient you are meaning to refer to which causes the smell. The smell is of mercaptans, sulfurous in nature. The thing that sparks me to comment is that all of these products are quite harmful (IX has a harmful classification) and they are skin sensitisers (above just 1% active, EU regulations would indicate the need for an irritant classification). IX is classified properly, but there are products out there which claim to compete with IX but mysteriously have no hazard warnings at all. So beware, if your smelly iron remover has no hazard symbol, it either has to have low levels such that it doesn't get classified or it has been classified incorrectly.