The lowest Cd number I've seen associated with Aptera is 0.11. The front wheel drive versions had 0.15.
The pre SO-1 versions did not have stability problems, or at least the PP range of prototypes did not. The Zen model with rear wheel drive was quite a bit taller, so it may not have been as stable.
The PP-6 or so was the best of the bunch:
Goin' with the Flow: Aptera 2e - Gallery