Checkbox Cross Sell allows your customers to add additional items to their cart when buying another item, merely by ticking a checkbox. It's like Impulse Buy for the Product Info page.
Here's what the product info screen looks like with Checkbox Cross Sell:
Only specific products (i.e. not categories) will be presented as cross sells. Items are selected from your Better Together configuration as follows:
The item will then be shown under the following conditions:
To emphasize this point again: items with non-defaultable attributes cannot be displayed as cross sells by Checkbox Cross Sell.
(Note: Products with defaultable attributes may be used, if you have installed my Default Attribute mod.)
For more information, please visit this product's webpage.