If the card is a good one, 16 to 128gig cards generally work fine for camera work in class 10 or U3. Formatting helps. I prefer a 32 to 64 to avoid storing too many videos and photos on one and since I download the files after a day's flying there's no need for a mega storage card. I also don't lose as much product if I lose a card, which has happened. The only corrupt video files I've obtained occurred when I forgot to stop a video before landing. For firmware upgrades you want to always use a 16gig card, especially for a -16 upgrade, so save the one that came with your bird.
A lot of people go on line and search for the cheapest card they can find on E-Bay and Amazon, paying no attention to the brand. They often get what they pay for. There are a lot of cheap cards that start life deficient in many ways, just as their are counterfeits and those that lie about storage capacity. There are some goods deals out there but those are outnumbered by those that are crap to begin with.