ServiceNow Bi-directional Integration Implementation to a third party?

[JPGServiceNow]

My company's customer uses ServiceNow. We provide service through our helpdesk.
I have to integrate my customer's ServiceNow into our helpdesk.
My company can't afford the ServiceNow TPP program to create a ServiceNow App.
Can I create an integration in my PDI and install it to test in their DEV/TEST (like AddtoUpdateSet from "Share")?
Which scope is best while creating this integration, Global or Scope?

Thanks in Advance.

#ServiceNow @ben_hollifield 

[Dr Atul G- LNG]

Hi @JPGServiceNow 

That is not recommended to create App in PDI bcz there can be some plugins which not available, also you cant publish the App in PDI.