You can update most flashcarts via the computer (I don't know any that you can't), that is, if you're talking about the OS and not the Firmware. But why get a Supercard DSONEi when you can get the 10x better DSTWO?
OLED's can get away with a lower peak brightness and still provide punchy HDR because of their contrast ratio. Like I said human vision is logarithmic. The higher the peak brightness the diminishing returns in perceived brightness.
@The Real Jdbye Oleds hit around 750 nits nowadays. The difference between a 1000 nit and a 750 nit isn't huge. It's only about a 4% increase in perceived brightness. Not huge at all. You'll need at least 2000 nit displays to notice a bigger difference.