Sorting products in woocommerce is... interesting. There's not usually much use for 'orderby=menu_order', except for displaying featured products. So you mark a bunch of products as 'featured' and go to sort them and ... oh crap, now you have hundreds of products across dozens of pages and the drag 'n drop sorting is totally useless!
This function will filter out all the 'non-featured' products when you go to sort them, and it makes things so much better.
You're welcome.