A:Answer My experience has been that I am able to use the wireless headset with manageable effort with only a single ear piece in place.
My ears are small and so ear buds do not work well for me. This is part of the reason I chose the Plantronics - BackBeat Fit wireless head set. The ear buds are comfortable but, are supported and stay in place from the behind the ear piece as well. The earbud and behind the ear piece along with the behind the neck are all one piece which is a nice design.
I work out with a trainer,and often leave one ear piece out which allows me to hear the music and my trainer at the same time. If I'm doing high-impact activity this doesn't work to well, but, for squats, dumbbells, it is fine.
With both ear pieces in place, it's very difficult to hear persons speaking to me or other noise. This is a great feature in my opinion because that's my intention to block everything out and listen to my music. if my music volume is lowered, I can make out conversations if I'm looking straight at a person.
I'm also able to answer calls while working out using my headset. This has been an added bonus and easy to use.
I hope this helps.
John