Do not buy cheap off ebay. There are so many scam sd cards it's just not worth it.
How the scam works: buy old, cheap, low-capacity cards. Hack them so they tell the device they are high capacity cards. Repackage them so they look like the real thing. Sell at a "bargain" price that's still a lot more than they cost (put up a load of fake feedback so your seller has a good rating too). Of course once the buyer exceeds the real capacity of the card their data is corrupted and lost, but that's not the scammer's problem...
And the brand isn't a defense (though in a genuine card it's a good sign), as these people sell fake SanDisk and Samsung cards. I'd just never buy an sd card from eBay.
BTW the class refers to the minimum write speed (higher = faster). You can read faster than you can write anyway. And TF (transflash) is an old name for the format which was later rebranded as microSD.
