Hello Tim,
Yes, the Recently Logged On Users and the Never Logged On Users reports use the Last-Logon-Timestamp property as the search criteria, and the Last Logon property isn't used.
The reason why we chose Last-Logon-Timestamp is that it is replicated across domain controllers, while Last Logon is not. So, in a scenario where a domain has multiple DCs, Adaxes would need to connect to each DC in the domain to build the report using the Last Logon property, which can take quite a long time. The Last-Logon-Timestamp property is replicated, so it will be up to date no matter which DC Adaxes is connected to.