Basically a keratin treatment. Most of the time when the product claims to be formaldehyde free, it just has a formaldehyde-cousin which releases formaldehyde as a byproduct from adding either heat or a chemical reactive, like formalin.
Or maybe it's got a glyoxylic acid active ingredient where it's just a step below a relaxer since the results can be permanent. https://www.ncbi.nlm.nih.gov/m/pubmed/24962464/
I always think of the long term effect of any kind of keratin/TMS/amino acid treatment on popular vloggers like Chime Edwards (Haircrush) and CharyJay