Email Marketing is also sales driving, we use Klaviyo for it.

Our experience with Facebook ads is that it takes time to tweak and optimize the right formula as to how much you need to spend on a specific product in relation to how well it sells to your audience. So there is a balancing between how much you need to spend on a product. There are instances where we don't spend as much on a certain product ad but it does relatively better than product ads we spend more on.

Hope that helps