I ordered two of these from Amazon. They are absurdly inexpensive, both worked great, and others with Nexus7s have also left good reviews. I bought them when they were $1, now they're 65 cents and shipped free. Shipping took about ten days to get to CA (they ship from Hong Kong).
Also, they picture a cable with a 90 degree micro USB, but I received one with a 90 degree and one with a straight USB. I swap back and forth between each and both are equally fine.
They work perfectly, they were $.01 each, LOL with $4.95 shipping from Hong Kong.
You need to be careful, if you bump them you could damage your usb port. Wish I'd gotten the one with the short cable rather than the dongle type. But oh well.
Make sure you get a USB OTG host cable. (I had previously thought that all USB OTGs shared that feature) I had gotten one without that feature, and it didn't work as I'd hoped.
Funny, the one I bought shipped with Prime, but stopped right after I placed my order. Amazon is getting rid of Prime with everything like under $6, and replacing it with some hoaxsy "add-on item" thing--they make it sound like those items were previously unavailable, but all they're doing is making it so you can't buy cheap things with Prime.. :/.