Disclaimer: I work with this stuff and might be a little biased to certain vendor solutions.
A good CGNAT implementations have support for static blocks: the subscriber always ends up a a specific ipnumber+portblock combination. (Each subscriber is assigned a specific number of exit ports and this all just logged once during startup so you always know where each subscriber ends up).
Should they run out of their assigned portblock, there are pools which you can borrow from (these need then to be logged who borrowed at what time etc). So all in all there is less logging than when everything was dynamic.
As for the long run I've read that the Gripen is cheaper to run.