push to talk
One thing I found helpful when I was merely profoundly hard-of-hearing was to use a push-to-talk switch that alternated between the microphone and HA output. Otherwise the feedback due to high gain was a real problem. The main downside was idiots who did not understand, even after explanation, that I was using push to talk. So I would finish talking and find the end of a sentence coming in. People can be so rude sometimes - always interrupting.