I tried some from Harbor Freight that I picked up for 9.99 and they were completely worthless. The biggest problem that I see is that wireless headphones really aren't made to broadcast a mostly quiet sound. In other words, 90% of the time for most detectorists, there is nothing to hear because most of us use our detectors in a silent discrimination mode. It is only when a target is found that there is any audio at all. Of course, if you are runnning in a non-silent all metal mode then your results would be different. But for me the issue was that the HF headphones would shut off automatically after 60 seconds if there was no audio going through them which just happened to be most of the time. And even when they stayed on the "quiet" moments really weren't quiet. They were filled with static.
In order for wireless headphones to work they need to be made to handle our type of audio signals which is NOT the same as your typical stereo music signal.