I've recently bought a micro SD card with 512GB for 20 euros from a Chinese site. Decided to take a chance and see if it was indeed possible to get so much storage for that kind of price. The result was OK. The drive is slow to read/write but does provide a real storage of 512GB.
What kind of tools can be used?
For Windows, this one might be your friend:
btw: Works also on Linux/Mac when using Wine.
For Linux/Mac command lines you have F3:
It seems the website has been offline, but it is possible to install the tool through any decent package manager.
apt-get install f3
brew install f3
After that be prepared to wait a long time since it will create 1GB files at the speed permitted by the card, which might take up to a full day to write.