I wonder if this has anything to do with the PSA merger...as what you've described there is literally the system from my wifes old DS3 circa 2014.
In the PSA system at the time you had a standard battery with separate lithium capacitor on the top.
If it is this system then the good news is it actually works because the main battery voltage has nothing to do with stop start activation (unlike the previous Fiat effort). The bad news being it is nothing everyone else isn't already doing and has been doing for years.
It also made no difference to the economy of the car it was fitted to iirc a 1.6 diesel that managed to produce 1mpg better economy than the petrol that replaced it. The petrol also has a similar system with the capacitor but they do not call it a mild hybrid because it doesn't have the reversible alternator.
The system I saw details of recently had the motor/generator installed within the gearbox casing. The fiat website gives little detail, but does suggest energy recovery happens while coasting, which needs the generator to be connected to the wheels, not the engine, suggesting their system is at the gearbox, not at the normal alternator position.
Of course, their definition of coasting might be different to ours. To me it is when the car is out of gear, or clutch down, so gearbox is disconnected from the engine. Difficult to see how an engine connected alternator will give anything in those conditions.