I will have an OG Xiaomi Mi Box and it's absurd how over the years it went from a purely functional media device to a complete shit show covered ads. Genuinely disgusted me every time I turned the TV on. I couldn't stand it anymore, I had to tear out the launcher with ADB and replace it with FLauncher.
I wish Kodi wasn't such a pain in the ass to deal with, especially for YouTube. We really need a new FOSS media center application. Until then, at least FLauncher works for now as a simple app switcher for a handful of Android apps.
You may already know this now, but I want to post it for those who don't because it's really cool and way ahead of its time.
That was for the VMU, the visual memory card. It stored your game saves but also some games had minigames you could play directly on it, often with bonuses in the main game. In the Sonic Adventure games you could take care of chao and such on it. That thing ate batteries like candy though.