I've heard that the EZ 3in1's rumble isn't very good. There is also the Ewin 2in1 and Ewin rumble (two separate carts). The disadvantage is that they are two separate carts so you have to remove the 2in1 to play rumble (no big deal since GBA games don't support rumble). The advantage is that the Ewin 2in1 has more memory than the EZ 3in1 and the Ewin rumble is better than the EZ 3in1.
Note that there are only a few games that support rumble anyway, and the rumble eats up battery time. It's kind of a novelty to try once or twice, but it gets old fast.
-Bri