Regular vitamin C may oxidize a bit before it’s absorbed, but certainly not completely, and you still receive a huge benefit from regular vitamin C. May I ask if a professional person told you this?
Buffered vitamin C has added to it a type of ascorbic acid which is able to unite with vitamins and minerals in order to lessen the acidity of vitamin C when it reaches your stomach. Some of the substances usually added to vitamin C to make the buffered type are sodium, magnesium, potassium, and calcium. This is especially true with a Candida albicans infestation since acid is actually part of the treatment. Also, the one you linked to is powder form, the pills are much easier to take and you can take them with you easily if you’re away from home during the day.
It isn’t necessary to pay more for a vitamin C just because it’s buffered, and personally, I’ve always used regular vitamin C. You can pick these up at supermarkets and pharmacies usually much cheaper than purchasing online; at least you can in the USA.