Third Party Batteries and Battery Grip for D7000

I looking to buy a couple of back up batteries for my D7000 and possible a battery grip too. I see quite a few 3rd party accessories on ebay and I'm wondering if these are worth getting instead of the expensive official Nikon ones. For example, the MB-D11 battery grips are over $200, but a 3rd party one on ebay is only $60.

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M.K.
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