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>> Variant B improved conversion rate (CVR) or Add-to-Cart (ATC) rate? Roll it out.

Basing rollouts on add-to-cart rate is generally not a great idea, particularly for experiments on product pages. There are a variety of reasons why shoppers add products to carts that may only be loosely based on intent to purchase. In my years of ecommerce A/B testing, I've seen plenty of tests that improve conversion rate and/or revenue per visitor but negatively impact add-to-cart rates.