These cards are on for $15 at Amazon this week and there seem to be two versions available. The older version listed as a U3 card and the newer version listed as a U1. Just wondering if anyone has experience with these specific cards and how they handle 4K video? The spec listing is rather confusing especially considering the backward jump from U3 to U1. Looking for some actual real world experience with video (4K) and stills. Thanks.