Worst Cosmetic - COSRX The Vitamin C 23 Serum

[COSRX The Vitamin C 23 Serum] is the worst cosmetic product I have ever used.

The reasons are, first, the user experience, and second, the smell.

Sometimes I feel a slight stinging sensation when I apply it, so I am worried it might be irritating. Also, when I apply it, there is an unfamiliar smell, like metal, so I am reluctant to use it.