Hi Paul,
Listing Alerts on a listing is dynamic and will display rental or property based on that listing type. The settings are for default shortcode operation instead of having to output a really long shortcode with a lot of options.
We are working on a CRM to better work with Listing Alerts which will allow for better data capture and subscription modification.
Currently Listing Alerts does not support price change tracking as the end user would end up with a lot of emails and eventually unsubscribe. Until the CRM is released there are a number of limitations with Users in WordPress. Our goal is to use the contacts (crm) as a post type so we can add this extra functionality.
Currently working on a number of extension updates and the CRM which can then further enhance Listing Alerts.
Will check the merge fields.