OmniFocus 2 has a single download file that accepts both Pro and Standard license keys. Pro features are unlocked when the appropriate license key is entered, but the application will still be named OmniFocus in the Finder, Dock and Menu Bar. After entering your Professional license and restarting, you should be able to confirm that you’re running Pro from the OmniFocus menu. Click About OmniFocus, and look for the purple text box that states OmniFocus Pro Upgrade is purchased & installed.
You can also confirm that you’re using Pro from the Licenses… window, accessed from the same OmniFocus menu. At the top of the window you should see Software Licensed: OmniFocus Professional 2.
To compare, here’s what the About dialog looks like in Standard:
And here’s after unlocking Pro: