I have one of these works fine no probs in my Rockchip aPad. Transcend Class 6 retail packed and genuine. Only one I have so can t tell you if the extra speed is worthwhile. It was nt much more expensive than a class 4 so I got it. 16gb is suppose to be ok but again not tried myself.http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140424021796&ssPageName=STRK:MEWNX:IT