The following extensions can be used by both Prevent Direct Access (PDA) Gold and Password Protect WordPress (PPWP) Pro:
- Campaign Monitor Integration
- ActiveCampaign Integration
- The integration with PDA Gold is still a work in progress
- MailChimp Integration
- Multisite Integration
- Statistics
In other words, you will only need to purchase them once and be able to use them on either or both plugins.