Class 10 and UHS1 presupposes a minimum sustained write speed of 10MB / sec. On my internal USB2,0 - card reader I have with ChristalDiskMark 22,35MB / s read speed and 19.34 MB / s write speed. (1000MB sequential) For me, absolutely satisfactory, especially for the price of 12th Long-term experience I have not but should bless the early time one of the cards, I'll mention it here anyway.