I'm using an inexpensive ZTE Maven 3 smartphone. I've been using the Plantronics 10 for a few weeks. The volume is very good. The speaker cut out a couple of times, but for the price, that's acceptable to me. I change every night, so I can't comment on the battery life. I tried the M50 and the volume was too low for me to hear. M 20, which I used before, did not play media files. As I said, I've only been using it for a while, so I can't say how long it will last. Update: Now on April 18, 2019, the speaker turns off randomly. It initiates a call and when the phone rings, the handset turns off. I have to fish my phone out of the pouch I wear on my belt. It's very inconvenient when I'm driving. I am a professional driver and need a hands-free system. I can't do this while driving with a customer. I'm reducing my rating to 3 stars.
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