actually I have an ezflahs 3in1 but I'm not using it much .. I would like to have one I could play on my actuall gba XD and I wanted do stuffs like the communication with gamecube .. I Know if you do it ingame (like sonic advance ) it would work, but if it need to load your save I'm not sure if will work :/ some gba games are jard and expensive to get, if this works would be great :B lol
And actually you can't do ez3in1 to original game, unless you use an code or something , I saw you need a modded DS rom to make it work :v
its the same deal with ez iv.. can do communication ingame.. (if the link works, and i am not sure about it)
you can use a 3 in 1 in a real gba if you get a GBA SHELL the only thing that prevents from working on the gba is the pastic part.... you can try to open a gba cart, and try to fit it inside...