Sharing records with Customer Community Login users

The article that you linked to is really for an alternative approach to using Sharing Sets as that is using Sharing Groups which can be used for both internal and external users.

For internal users you can still use standard Salesforce Sharing Rules as well as Sharing Groups based on criteria on the custom object.

To define the sharing set rules for a Customer Community User you would need to pick a common value for both the user and the custom object. Often this would be the Account as a the community user is related to an account by their Contact record and the custom object would then also need to be linked to a record that has a link to the Account.

Examples

1. Custom Object A has a lookup relationship to Account so the User Account and Custom Object Account will match.
2. Custom Object B has a lookup relationship to Case and the relationship will be defined by the Case.Account field. So the user needs to be on the same Account as the Case to have access to the custom object. See the below image.

Example 2 can be done with any relationship that the Custom Object has with another object that has a relationship to the Account.

Sharing Sets benefits are that they permit sharing of records to High Volume Community licences that cannot use Sharing Rules or Apex Sharing.

Sharing Sets cannot be used as an alternative to Sharing Rules as they are not available to licence types that can use the rules such as Customer Community Plus or Partner Community users.

An advantage of Sharing Sets over Sharing Rules can be that they are easier to define as it is possible to setup a sharing set with criteria like

'User:Account' = 'Case:Account'

While for Sharing Rules it is necessary to create a separate sharing rule for each Customer or Partner Organisation (which will have its own Role) to share records owned by users with that Role with the other users with that Role, and say with cases if the ownership changes to an internal user or queue then access to the case could be lost, unlike the Sharing Set. This can of course be worked round by using Groups, but that adds a layer of maintenance to the SF Organisation setup.

Sharing sets do not seem to create a record in the sharing tables for the database as I have tried retrieving them using Data Loader and cannot find an entry that corresponds to the profile or other information related to the high volume licence types.