Zoho CRM Invoice vs. Zoko Invoice

Zoho CRM Invoice vs. Zoko Invoice

From time to time I'm wondering about obviously duplicated functionality across the Zoho products.
Zoho one seems only to be a menu of different applications; it seams that we have to deal with this.

We are using the CRM and now looking to use Zoho to create/put the sales documents (proposals, orders, bills).
But the question arises: Why is there Zoho Invoice?

What would be the workflow? Should we favor one over the other? Do we really need Zoho Invoice? It looks to be nice but comes with a ton or synchronization settings to connect the data to CRM...

I really don't see the concept of having two such applications, but if one is better, I won't care about the other.

Thanks