HubSpot's built-in integration with NetSuite is very limited.
For example, data type of properties in HubSpot are not same as field type in NetSuite. So it's very difficult to set bi-directional sync between them.
Due to this, per requirement of a company I have developed my own Integration solution between NetSuite and HubSpot which syncs
• Deal <-> Estimate (and Sales Order)
• Company <-> Customer (type: Company)
• Contact <-> Customer (type: Individual)
If you need such custom integration, I will be helpful on that.