There are only a few scholarly journals on this ingredient because sadly none are free, however they do note 3,4-Divanillyltetrahydrofuran binding affinity for SHBG. In one journal they state "All lignans except (-)-pinoresinol developed a binding affinity to SHBG in the in vitro assay. The affinity of (-)-3,4-divanillyltetrahydrofuran was outstandingly high" (1).
Another journal says the same, "Lignans bind to sex hormone-binding globulin (SHBG). The lignan with the greatest binding affinity is (+/-)-3,4-divanillyltetrahydrofuran" (2).
Although we aren't able to see the actual research done, this information from the abstract does state that 3,4-divanillyltetrahydrofuran attaches to SHBG. This shows that the claims are true, however to what extent is not known. Many people have ran sponsored/unsponsored logs of products with this ingredient and also had blood tests done showing free testosterone before and after, so if you would like to see some anecdotal feedback you could find those online.
1. Schottner, M., G. Gansser, and D. Spiteller. "Lignans from the roots of Urtica dioica and their metabolites bind to human sex hormone binding globulin (SHBG)." Planta Med. 63 (1997): 529-32. PubMed.
2. Schöttner, M., D. Gansser, and G. Spiteller. "Interaction of lignans with human sex hormone binding globulin (SHBG)." Z Naturforsch C. 52 (1997): 834-43. PubMed.