IMHO, it is definitely worth using one of these programs to verify EVERY SD card/flash drive you buy, no matter where you buy it from. The retailer, not knowing the difference, then (unknowingly) sells the (fake) card to someone else. There are tons of fake cards out there and some even come from reputable and authorized retailers (my guess is people buy them, take the real one, substitute it with a fake one (which is a forgery even down to the outer packaging), and return it. If it is unsuccessful in reading this data, it is an indication that you may have a defective and/or a fraudulent media device-combined with a speed test that shows vastly slower speeds than advertised by the maker, this is even more suggestive of an issue.) (Effectively, this program writes data to fill up the entire drive and then attempts to read that data back.

I use H2TestW, but this is a Windows legacy program. There is not a great solution for Mac beyond manually creating a file the same size of the SD card, moving it to the SD card, and then verifying the files copied over and are readable.

Fakeflashtest mac