Adding a buy now button on the product list is potentially significantly worse than an add to cart because you're taking them to checkout immediately where the purpose is to get them to get them through the funnel fast. I anticipate people abandoning if they go through the list page to checkout because they won't know what they are buying:
You should not add those buttons because of many reasons:
- Customer needs to understand what this product really is before commitment.
- What if they want more than one? Are you going to clutter the page with a quantity field too?
- What if they want a different option(s), going to add that to the page as well?
Be careful with breaking conventions because they are normally placed there for a reason.
I wanted to emphasize why you should stay away from buttons being present on the list page:
Flow will be the same: users will still find themselves going to the product page for more information and other utilities to potentially enhance their buying experience (whether adding more, changing style/colors, etc).
The only time you will ever show a button is if the user has already purchased this product, become familiar with it and just wants to re-buy it. In that case, a button could potentially be viable. Whether it is hidden or not (and hover reveals it) is irrelevant, users will still want to go to the product page for more information before purchasing.