| Primary purpose | Rank Amazon listings by computed price per unit before you pick. | Apply coupon codes at checkout. |
| When you use it | Before adding to cart. At product-discovery time. | At checkout, after you've already chosen everything. |
| Where you save | On the listing itself (a cheaper-per-unit alternative in the same category). | On the cart total via discount code. |
| Typical savings | 20% to 70% by switching to a cheaper-per-unit listing. | 5% to 15% via a coupon code. |
| Coverage | Amazon US, 50+ categories. | Many retailers; coupon codes vary in availability. |
| Browser extension | No. Standalone web app. | Yes. Auto-runs at checkout. |
| Account required | No. | Yes for cashback rewards. |
| Affiliate transparency | Source is public. Commission does not affect ranking. | Owned by PayPal. Affiliate revenue model. |
| Cost | Free. | Free. |