This release adds support for micro SD cards via Serial Port 2 on GameCube consoles where that port exists. It requires a small PCB and the compatibility/speed is the same as using an SD card via the front memory card ports. The main benefit is that it leaves the 2 front slots free for a memory card and any other peripherals you might require in games.
https://github.com/citrus3000psi/SD2SP2
That being said, the alternate read patches (which are now the default) have basically been rewritten by @Extrems since the last release and should be much more stable and compatible. 2-disc support has been added into these patches but audio streaming is still only available via the old non alternate patches for now.
https://github.com/emukidid/swiss-gc/releases/tag/v0.4r682

https://github.com/citrus3000psi/SD2SP2
That being said, the alternate read patches (which are now the default) have basically been rewritten by @Extrems since the last release and should be much more stable and compatible. 2-disc support has been added into these patches but audio streaming is still only available via the old non alternate patches for now.
https://github.com/emukidid/swiss-gc/releases/tag/v0.4r682