Continuing on my path to enlightenment, I’m thinking EZKeys 1 doesn’t need to be authorized anymore, but instruments do.
This would mean that you can use EZKeys 1 on any number of computers as long as you authorize an instrument with it (while each instrument can be authorized to two computers).
On the other hand, it seems EZKeys 2 can only be used on two computers as it has two authorization slots.
Strangely, EZKeys 1 used to have (two) authorization slots before, but they’re now gone. After downloading EZKeys 1, it simply asks for an instrument to be added (and authorized presumably).