I have ISY on 5.0.4. When I select Upgrade Z-Wave Firmware, a warning box pops-up which says that I need to shift the primary to a different controller. What does this mean? Do I need to buy another device? What kind? If I shift primary to another device, upgrade firmware on ISY, then what? Do I need to move back primary to ISY?What would I lose in this movement? Is this movement of primary an ISY thing or is it with every Z-Wave controller?

Yes, you need to change the primary controller or exclude all your devices. But, why are you attempting to upgrade. You should already have the latest version if you've been using Z-Wave devices.(which is 21110).

I want to be prepared in the event that an upgrade does come out. What kind of device would I need to shift the primary?

Any Z-Wave controller.

Thanks, Do you happen to know if Aeon Labs Z-Stick would work?

I used an Aeon minimote, but I believe a zstick *should* work.