Getting a bit Off topic from the original posted question..
but I have seen the GSE vs Vit C comparison before, here's one website with info....
[Grape seeds contains mainly phenols such as proanthocyanidins (oligomeric proanthocyanidins). Scientific studies have shown that the antioxidant power of proanthocyanidins is 20 times greater than vitamin E and 50 times greater than vitamin C.]
https://www.liebertpub.com/doi/pdfpl...31?src=recsys&