That depends on which of the 3 functions you're talking about.
The browser support will work with any slot 1 cart, you just need to patch the browser rom.
The apps that allow for GBA functionality should work on any flashcart that has DLDI support, so they should work with the Real.
The rumble would require a bit of messing around. There are two ways to enable the rumble on a slot 1 cart that doesn't support it directly:
- Patch each game you want to use rumble with (this can cause glitches, or just not work).
- Patch some small game (it doesn't matter if the game uses rumble), start that game to put the 3-in-1 in rumble mode, soft reset back to the Real's menu, then start the game you want to use rumble with. Once the 3-in-1 is set to rumble mode it will stay that way until the power is turned off.
And no, I've never used the M3 or G6 Real, but I have a good bit of experience with the 3-in-1.