As per this post: https://community.developer.atlassian.com/t/alerts-api-inconsistency/92982 it would really help the customers if they could also receive the extra properties' values in the List Alerts API results.

This is because, currently they have to run the List Alerts API to get a list of all the alerts and then run the Get Alert API individually for each alert to get the extra properties' values on them as well.