Shopify app fees for product sourcing app

[MVos]

Hi Shopify Dev community, 

I'm looking into developing a Shopify app for product sourcing. Customers of the app would pay per product that they order through the app. 

Now, I have found on the Shopify Partner website that Shopify usually takes a 20% commission on app sales. However, as per this article product sourcing apps are exempt from the Billing API. Does this mean that Shopify does not take the 20% commission? 20% would be a very hefty price to pay as there are a lot of costs associated with physical products as opposed to software. 

So, if anyone here knows what the exact fees are regarding product sourcing apps, please let me know!