Big thing is that it saves permanently automatically. With the 2.5 you need to hit reset for the saves to persist.
It also has an RTC so you can play Doubutsu no Mori and Pokemon Stadium 2.
Edit: Actually Krikzz has you covered:
I'm still not sure whether the saves are stored on the SD card or if I still need to use a Memory Pak, which one is it? Thanks for the fast reply.