NeoFlash
I wrote a new NeoFlash flashcart guide. I spent three days wrestling with it to figure everything out, and there are still options that don't work (or that I couldn't figure out).
NeoFlash is an amazing cartridge. It does its main job — running NDS and GBA games — perfectly. But the software for writing games to it was clearly made by people who had no idea what they were doing. That's the only way I can explain all the bizarre things that happen in NeoPower Kit. It crashes, throws errors, and a lot of its features simply don't work. For example, with GBA games you can enable an option to return from a game to the cartridge menu. Do that, and the games stop launching entirely. I wanted to exit games back to the menu, not make it impossible to launch them from the menu in the first place.
There is very little information about the cartridge. The developer took a rather creative approach to documentation: they saved a forum post written by an ordinary user as a web page and put it on the disc. And the instructions are basically “click Add to add a game to the program, click Burn to write it to the cartridge.” A true masterpiece of technical writing.
So, in this whole setup, the NeoFlash cartridge itself is the only thing that works properly. Everything else is awful.