Brightness is adjusted at the bottom Left side of the bottom screen, 3 or 4 Horizontal bars.. someone else will have to let you know about newer DS lites and the carts as im not sure
I traded in my original DS for a new DS lite about 6 months ago and a friend of mine got a new DS lite for christmas. The M3 real works fine on both of those. Havent heard any reports of newer ones not working.