a stanalone GBA Expansion Pack comes with replacement shells rarely available in the perfect bundle, so all you have practically done is wasted a little money on RAM in the Rumble Pak.
I myself bought the Rumble RAM pack and the GBA Expansion seperately myself, as it was only €5 more than rumble+GBA, which in turn was €.05 less than the perfect bundle (complicated stuff if your supplier of choice cannot get his prices right), thinking that it would not hurt to have additional RAM on the Rumble Pak, not knowing that the Rumble Pack sucked even worse than the 3in1 and that the Rumble RAM RAM is barely usable for anything but Opera, including Sakura, which only detects 2 MB, although the Rumble RAM Pack should supply at least 8MB, as the Browser expects that much, for the official Memory Expansion Pack supplies 8 MB, and DSLinux, which detects 32 MB and obviously fails, and now this sentence is extremely long and I do not want to end it yet and so I write on and on and on.