There have been quiet a few threads about this but the m3 simply and R4 are exactly the same thing. but i must tell you now that the moonshell app is not great for movies because it is only compatible with dgp.
No you do not need a slot 2 cartridge for movies, the m3 simply/R4 can handle it well with moonshell (a multimedia application that is built in, allowing you to play music, movies, pictures, and read text files). i guess because the emulators are still in progress.i fine it fun though, with main games working well like mario and such. they are great for the games that work, but some snes roms dont work with some emulators.