It is a bit of a worry that car with speed sign recognition can suddenly decide to slow down without at least putting brake lights on.
This is not a jab at you culzean, just a general comment.
It's not breaking, it's just slowing due to lack of accelerator use, just like my driving instructor told me to do as I was approaching a reduction in speed limit. In that way you are naturally down to the speed limit as you pass the signs (which is what you are supposed to do by law).
It has been argued elsewhere on the forum that you should avoid using the brakes to save fuel and general wear and tear.
I personally don't see such a driving style as dangerous in any way. The person behind should be two seconds distance, minimum and paying attention to what is going on around them.
The reason I posted the Audi link is that it shows that the Audi (and probably all systems) suffers from reading ( more likely misreading) speed limit signs that get picked up, normally on adjacent roads, these can be posting a considerably lower limit and cause vehicle to slow down without warning following traffic via brake lights.
Also on the Tesla forum, if the auto drive system loses some of its normal 'cues' e.g. lines on the road, or picks up things that are not normal road lines but it sees them as such the car can do stupid things like swapping lanes or even going to other side road. There are also cases where Tesla system has not 'seen' things like vehicles have stopped ahead and would have ploughed into them at full speed had the driver not braked the car manually. These auto systems are far from sorted.
As for using engine braking to slow a vehicle rather than brakes - this may be good for fuel consumption but I was always told that brake pads are much cheaper than gearboxes, and the gears, bearings and CV joints wear as much from slowing the cars weight down as they do from accelerating it.