For those of you looking for a great, slim flash drive for your Wii for USB Loader GX, I think I found the perfect one!
I recommend the "PNY - 256GB Elite-X Fit USB 3.1 Flash Drive - 200MB/s". I bought mine from Best Buy.
The reasons I think it's perfect:
1. It works flawlessly.
2. It's slim and is easily hidden behind a Wii, and won't accidentally break off if something hits it like larger USB drives might.
3. It's cheap.
4. It's the perfect size for flash storage and will hold at minimum 30 full-sized dual-layer Wii games (but will actually hold WAY more especially if you're using GameCube, I have ~80 Wii + Gamecube games and it's not even full). If you want way more storage than that, you should probably move up to using an external hard drive instead of a USB flash drive.
5. It's USB 3.1 and thus is SUPER fast to add or remove games from using a compatible computer.
I added it with more information on the Wii USB Compatibility Wiki.
If you get it and try it for yourself, please update the Wiki with a confirmation.