Buy the Dove Damage Therapy Derma Shampoo Dryness + Itch.

It is cheaper per ounce, backed by thousands more scalp histories, and you can actually buy it right now.

What was compared

1. One of these you can't even buy
First Aid Beauty's listing shows currently unavailable with no restock date, so it is not a real option today. Dove ships now at full price, which makes this comparison shorter than it looks.
2. Nearly 40x more scalps have tested this
Dove sits at 4.6 stars across 7,995 ratings, FAB at 4.3 across 215. A sample that small can flip with one bad batch of reviews, Dove's score is already proven stable at scale.
3. More bottle, less money per wash
Dove is $28.99 for 12 oz ($2.42/oz), FAB is $31 for 8 oz ($3.88/oz). You get roughly 50% more shampoo for a lower per-ounce price, and that gap compounds every time you wash your hair.
4. You know exactly what's fighting your dandruff
Dove lists Pyrithione Zinc, a well-established over-the-counter dandruff active, right on the page. FAB's listing never clearly states its active ingredient, so you are trusting marketing copy over a named compound.
5. Yes, some swear by FAB. Buy Dove anyway.
A few glowing FAB reviews call it life-changing, but that is 215 people against Dove's near 8,000, and you cannot even purchase FAB right now. Unless you specifically need its calendula formula for color-treated hair and can somehow find stock, Dove's proven, available formula is the safer bet.