I bought a 32Gb from ebay auction for $11. It had similar problems. Would save files to it, but kept umounting and would dump all the files on it to lost.dir. They all had broken file extensions and the filenames were garbled. I since just play it safe and stick to sandisk sd cards from amazon.
The Extreme cards are mega expensive, but from time to time my local BB has incredible sales on them. Watch the site. I actually check every couple of days for the sales as I tend to buy things I might not need now, but will appreciate someday, lol.
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