Here is a link to the Bluetooth headset that worked best with the #AnyTone878 / #AnyTone878uv - as mentioned in the test results above ~ https://www.walmart.com/ip/Blue-Tiger-Elite-Plus-Single-and-Dual-Ear-Wireless-Bluetooth-Headset-Noise-Cancellation-with-Microphone-Long-Battery-Life/113104679

... Second Place: The #AnyTone878uv HT's attachable handheld speaker-mic - also set at Analog-Mic-Gain setting 2 - which was slightly quieter and slightly less clear sounding than the HT's internal mic. Of the two Bluetooth headsets, the BlueTiger Dual Elite Plus - at Bluetooth Mic-Gain setting 4 - was far superior to the other BT headphone, just a bit quieter than the first two mics. (... more results in the comments below)

Did a simplex test on 2meters today w/ two other local hams who helped me determine the best Bluetooth headset (of two I own) to use w/ the #AnyTone878uv, as well as which mic gain settings sound best w/ HT's internal mic, an attached handheld speaker-mic, a BlueTiger Dual Elite Plus headset w/ swivel mic, & a BT-940 Bluetooth headphone w/ earpiece mic. Results: HT's internal mic was best of all - at Analog-Mic-Gain setting 2. Second Place: (...full results continued in comments below) #KE0FFT