Does this mean Android devices should not be used until they get this update?
They can be used without issue. Besides, this update is strictly for Nexus devices, not all Android devices.
What without issue? Man in the middle attack if the application uses Android's OpenSSL?
And that the update is only available for Nexus would mean all the others stay broken.
This is a minor update that looks for the OpenSSL vulnerability and if found inserts patch. Why isn't the update going to all devices. Probably because it would take longer and cost more money for any carriers to bother, since 4.5 will be released next week.
Motorola had started rolling out 4.4.3 and now they they have to go back and say 4.4.4 will be available in 3-5 weeks.
Samsung is supposed to start releasing 4.4.3 on some devices very soon, but now I don't know what they will do.
I guess I will have to leave my brand new TabPRO in the box.
Apple 1 - Android 0
Yep, leave it in the box. In fact, you should never touch an Android device.