Features - WP Developing

Is it possible to have a free listing option and then a paid option that includes more fields for the same listing?

Yes, by disabling certain fields on the free plan and then enabling them on the paid plan.

This is not planned. One may be able to use booking plugins from third parties to integrate with Directories Pro.

It can be used for a single site with multisite but cannot be used across multiple sites using multisite.

Yes.

While this functionality is available in Sabai Directory, it is not currently available in Directories Pro.

No.

Sabai: It can only be used on a single domain.

Me: The answer from Sabai Apps is unclear about subdomains, however, I have used it on subdomains for testing purposes and it seems to work fine.

This is not currently possible.

Yes, through integrations with third party plugins – currently Contact Form 7, WPForms, and Gravity Forms.

There are a number of differences between the two products. They are not based on the same code, Directories Pro is a complete rewrite.
One significant change is in the increased use of WP’s built-in tables rather than custom tables to provide smoother integration with other plugins (e.g. Yoast SEO) and core WP functionality.
There are some features in Sabai Directory that are not included in Directories Pro and vice versa. For example, Directories Pro does not currently support using the OpenStreetMap API and there is no current plan for myCRED integration as is available with Sabai Directory.
While Sabai Directory is still actively maintained, most development is going into Directories Pro.