Thanks Laura... That explains it!
I just spent another hour testing out the test drive file (on an older Mac with a larger screen)... and still couldn't find the Out of Scope Tax option. I thought maybe I had missed the option on my smaller screen. Apparently not!
This OoS option is especially crucial as when I add a Discount line to the invoice I made in Test Drive, it did not allow me to save the invoice until I attributed a tax code... and as there was no option for OoS I was stuck...
If you can assure me the OoS is in the live version of QGO I don't think I need to run a trial version before diving in. I'm still playing around with a few other features but so far it looks like a match.