Do you lose sales when products go out of stock?

I’ll be straight — I built a Shopify app and I’m here to get FB, not sell.

It helps recover sales from out-of-stock products by showing better alternatives instead of a dead “sold out” page.

Before I launch, I want real opinions:

Is this something that would actually help, or do customers just leave anyway?

Happy to show it if anyone wants to take a look.