Got this free with a Sony Ericsson Xperia Mini Pro phone.
This device announces to the thing it plugs into that it requires up to 500mA. In case you don't know, that's the absolute maximum current that USB can supply - it's enough to power things with motors and charge device batteries. A MicroSD card itself needs at most about 100mA. There is no way this device really needs that kind of current draw, it's just sloppy design. I've seen comparable SD adapters declare a max of 250mA.
This will most likely cause no problem if you're plugging this into a traditional PC, but what this means is if you plug it into a USB On-The-Go device like a media player, phone, or tablet it will not work because of its stated unnecessarily high power consumption. So fine for PC only use, but avoid if you want it to 'just work' everywhere.