Marketa is built around the two pages that decide whether a shop makes money: the product page and the checkout. Both load in under a second on a mid-range phone, and neither asks the customer to think about anything except the thing they came to buy.
Conversion-focused eCommerce theme. Tested against the current WordPress release before every update, and against the two before it.
WooCommerce templates are styled to match the rest of the theme rather than overriding it, so a plugin update never leaves the shop looking like a different site. Stock, sale and back-order states all have their own treatment.