Has anyone used uSync Migrations to transfer content within the same version of Umbraco, rather than upgrading from Umbraco 7.x to a newer version? I'm particularly interested in whether it's feasible to migrate Nested Content items to Block List, moving from one v13 site to another v13 site.

Yes you can do that, the "convert" option is the dashboard let's you convert the current site files

Amazing... thanks for the quick reply!