I got a SFC30 controller thanks to this thread, and I love it. Except that I was kinda annoyed that 360/XInput mode didn't work for bluetooth modes. I'd much rather be cordless; but games work much, much better with it. (Also I couldn't get it to work on USB either; apparently they removed it to make space for Wii mode.)
So I wrote a simple app that takes the input and emulates a 360/XInput controller. I've only tried it on Downwell and Shovel Knight, but it works great! Also has a higher compatibility as you can swap between the arrows working on the d-pad or left stick depending on how the game originally worked. And as a bonus: you can swap between using the buttons as labeled, or swapping A/B and X/Y so that the physical layout is the same as the 360's. (Thus remapping B to be on the right instead of the bottom.)
Just open and leave minimized in the background.
https://github.com/ROFISH/FC30XInput/releases
(For Bluetooth, use the hidden START+R mode for full joystick, the default START only method puts the control pad as keyboard arrows, which is annoying and can't capture.)