The last time I bought these from Woot, all 3 were defective. And in the worst way - I gave them as gifts, and within a couple of weeks they started misbehaving. One of the units stopped charging almost immediately out of the box. The next one, the microphone sounded so quiet that it was lower than a whisper (I gave that one to my best friend, we talk everyday on the phone). The last one, I forget what the problem was, to be honest, but that failed as well.
Just buy new ones. Seriously.
I actually have been liking mine and was considering getting another.
The only gripe on mine is that while just after taking it off the charger it says “7 hours talk time” as soon as I use it for an hour of talking it then says “4 hours talk time”. I think I can get about 3 or so hours out of the battery but I generally only use it for one hour conversations at a time.
Overall I am happy I bought one but a brand new Legend is only $65 at the mothersite. I think I will roll the dice again on this one. If it is bad (to a non functional level) it does have a Woot 90 day warranty.
I started using Plantronics Headsets back in 1972 when I was working in the control towers and radar rooms. Plantronics was the only gig in town and was 100% reliable…ahead of their time with noise cancellation. I wouldnt own anything but a Plantronics headset.
I purchased an M50 last year and was pretty satisfied with it . . . until it ran a cycle through the washing machine. It now only turns on when I plug it in. It works off battery afterwards but one I slide the power switch off, it’s off until I plug it back in.
Overall, my experience with this refurb is positive. Battery lasts long.
I just wouldn’t recommend washing it! 
I’ve owned a number of but headsets over the years, including Jawbone. The Plantronics Voyager Legend is the best I’ve owned by far. If you get one, buy the charging case! Great products, both.