The toxicity of vanadium depends on its physico-chemical state; particularly on its valence state and solubility. Tetravalent VOSO4 has been reported to be more than 5 times as toxic as trivalent V2O3 (Roschin, 1967). Vanadium compounds are poorly absorbed through the gastrointestinal system. Inhalation exposures to vanadium and vanadium compounds result primarily in adverse effects to the respiratory system (Sax, 1984; ATSDR, 1990; Ress et al., 2003; Worle-Knirsch et al., 2007).
Powdered metallic vanadium is a fire hazard, and unless known otherwise, all vanadium compounds should be considered highly toxic. Generally, the higher the oxidation state of vanadium, the more toxic the compound is.
i know its from wiki, so its not 100% reliable but take it as you will
And the problem with vanadium as with most other heavy metals, is that it can accumulate.
So while you may rely on data stating that one single dose of 60 mg was not found to be toxic, we are not talking about a single time ingestion of the compound, but rather long time supplementation. Which means that if it does in fact accumulate, it will build up to toxic levels over time and cause problems id rather not deal with.
So personally ill pass on this "supplement", there are more effective insulin potentiators, such as K-R-ALA for example.