This has nothing to do with the Stingray devices though.
Apple can certainly decrypt any iMessage, as explained very thoroughly in the article you linked to.
If Apple can decrypt them, then law enforcement can decrypt them, so they don't really even need the Stingray device.
Nobody knows whether or not the NSA stores all iMessages. They certainly can, and from everything we've seen if they can, they do, so if you are concerned about privacy you have to assume that they do. The thing about the NSA databases these days is that they allow multiple governments and other government agencies to access that data.
Imagine how many peoples lives would be "ruined" if someone took that data and published it on the internet, "here is every iMessage for the past year".
Apple can certainly decrypt any iMessage, as explained very thoroughly in the article you linked to.
If Apple can decrypt them, then law enforcement can decrypt them, so they don't really even need the Stingray device.
Nobody knows whether or not the NSA stores all iMessages. They certainly can, and from everything we've seen if they can, they do, so if you are concerned about privacy you have to assume that they do. The thing about the NSA databases these days is that they allow multiple governments and other government agencies to access that data.
Imagine how many peoples lives would be "ruined" if someone took that data and published it on the internet, "here is every iMessage for the past year".