Dave ...
Yep, every Y6 or multirotor is going to be an individual, chaos theory rules.... too many variables. Actually it would be interesting to know how consistent Parrot Drones are since they are mass produced on a production line rather than built by individuals.
In the full scale aviation world, before fly by wire came along, every aircraft was an individual and a pilot had to be able to adapt accordingly. Despite gyros, accelerometers, gps and such, multi rotors are still in that world. Modern aircraft flying by wire present a consistent interface to the pilot who can confidently fly an airliner from 100 seats with 2 engines to 400 seats with 4 engines for as long as the airframe manufacturer is the same, the engines, however, can come from any of 3 manufacturers. I look forward to the same happening in our world but I don't expect that any time soon.
andy