It is possible to do cross App/Type comparisons?
No, is only possible to compare Items from the same App/Type at a time, however is possible displaying several ZOOcompare Modules with different configurations on the same page.
Is possible to upgrade from ZOOcompare 2 to 3?
Due to the big changes made in ZOOcompare 3 the upgrade process is not possible, instead a clean installation must be performed uninstalling any previous version. The comparison settings will be lost during this process, be sure to back up your data before proceeding.