My experience with being bumped for a voucher, but with Delta.
Three of us traveling for work and we're in Minneapolis, waiting for our last leg to our destination. Gate agent announces they're looking for three people to bump for $400 voucher. We start looking on the app to see what flights they have later in the day we can jump on, and see one about seven hours later. Gate agent bumps up to $600. We talk among ourselves and agree we will send one of us up and ask for $800 plus club passes. Gate agent says he can't do passes but will keep us in mind. About five minutes later he comes over to us and says he asked his manager, and though he can't give us club passes, he is authorized to give us the max they can offer, $1100, in a voucher. We jumped on it. So we got rebooked on the later flight, and since we now had hours to kill, took the train to the Mall Of America for the afternoon. Bonus was since we were traveling for work, we were getting paid while we waited for the later flight.