Haven't tried Vellus, but heard very good things about it. Another one to look into is Iv San Bernard - they are $$$, but have major sales a few times a year and that's when people stock up.
Stay away from Mink Sheen, as they do actually use mink oil in their products - and as we all know, mink farms are some of the most horrendously cruel places on the planet
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If you want a general vitamin, I'd buy from Natures Farmacy - excellent! As far as specifically for hair growth, the only thing I know of that really promotes that is biotin.