SOUND

Unfortunately, Bluetooth audio available only on Android side (smartphone, apps) and does not work on the RFinder side.
There's been chatter about RFinder creating a Bluetooth dongle for the RFinder side.

“Echolink is working for me. Make sure you select the volume icon on the group page and it is set to where you want the audio coming from. It is different than in the settings tab. Also the volume for echo is controlled by the volume on the right side of the HT not the Rfinder knob!” Source: Joseph Marco

“Echolink app uses the phone volume on the side and not the volume knob for the radio assuming you don't know..” Source: Kelly Londo

If using Mint Mobile and hearing slow speech, set the APN Protocol to IPv4.
On B1-Plus: Settings / Network & Internet / Mobile Network / Advanced / Access Point Names / T-Mobile US LTE / APN Protocol / IPv4

Feature added v13.26.
Available via OPTIONS button
To unboost, turn the volume knob counter-clockwise