I am asuming by legit you mean that the companies they carry are good qualiy not like other products you sometime buy online that you don't know where its coming from.
Actually if you compare prices online I have found the Koshervitamins does come out a little cheaper then other online retailers and has a larger selection then most local pharmacies. Also as to why you would shop in kosher vitamins even if it does come out a few cents more is because they ship to you (if you are in the NY, NJ area UPS usally arives the next day!) and my opion is when you speak to someone there they actually care about what works for you, and dont just recomened the most expensive supplement they have.
I don't know of you're affiliated with the said website, but when I compare to local stores, they come out way more expensive.
I'm on DD to $ave dough...
I'm not locked up, b"h I go to brick and mortar stores, delivery is not important for something like (as light as) vitamins
As far as nutritional advice, there's so much available these days, and every other pharmacy offers a nutritionist on staff as well.
in contrast if they are taken to alleviate symptoms or to remove them than they would be akin to medicine
And IIRC, even so, it would still depend, and many still require a hechsher. Think something like Tylenol etc..