Anyone know if the back is kevlar?
Yes, the back is DuPont Kevlar with a soft touch coating.
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I wonder how they're measuring the "24 hour battery life" of the MX.
On their website, they just list it as "mixed use". I have to say, this is the first time I've ever seen a company actually state an expected battery life for actually using the device. Typically they will list a talk time and a standby time, and that will be about it. The fact that they go out of their way to say mixed use should last 24 hours is interesting to me.