All - thanks for the replies - I was thinking that, since both instances of ADBTuner were running on the same PC, that ADB on the Onn TV would see the attempted connection from the :experimental docker as coming from the same RSA fingerprint, but I guess that's not right...
EDIT: I tried using the exact same docker compose (at the top of this thread) same ports, except I put in the :experimental tag - I stopped the other docker first - the experimental one started up, but same thing - it wouldn't connect to the Onn Box
OK let me ask this another way - is the RSA fingerprint unique to a specific docker and tag, such that ADBTuner:experimental would appear different from the ADBTuner:latest version even if it is running on the same PC and using the same port numbers? If so, would I have to turn off ADB on each Onn box and then re-authorize ADB to the ADBTuner:experimental?