This will not work reliably in an S4.  After installing and formatting it worked ok for 2 days.  Then it began unmounting itself anytime it was read or written to, resulting in a card that doesn't work anymore.  Searching various Samsun and SanDisk boards shows neither company will fess-up to a problem.  Cannot say how good this is in anything else.  I may wind up returning this to Amazon if I cannot find any other thing it will work in... e.g. BD disk player or camera.