I just picked one of these
up at Amazon and thought I'd let you know about it.
While I wouldn't use this as my primary game controller (and it is a little pricey at $24.95), if you want something to use with your MIST on the go that is very
portable and that doesn't obviously look
like a gamepad, it is a decent little controller, especially for the size of it.
It has a lot of buttons and just shows up in the OS/core as a standard USB gamepad. While some of the Q/As on Amazon say that it will only work with Windows/MAC, I can personally vouch for the fact that that's not the case. I've tried it with a couple of the cores, and it works quite well for what it is. It comes with a retractable mini USB cable.
You may recognize the name of the company that makes it (or at least that put their name on it). It's ION, the same company that made the iCade mini arcade cabinets.
Here are a couple of crappy pictures of it both open and closed next to my MIST for a sense of scale...
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