Yea, V2 has hard save whilst V3 has quick save too (like a save state on an emulator). I don't see the need for this, you can't use save states on a real GBA game, so its like cheating in a way. If this idea interests you though, get V3. Its says it has "ROM Compression" on V3 as well, but with 1GB, you won't need it.
Basically, GBA roms come in a few sizes... 4MB, 8MB, 16MB and some which are bigger. These are the cart sizes, they are in Megabits on the website as thats what real GBA carts use, but Windows uses Megabytes.
128Mb = 16MB
256Mb = 32MB
512Mb = 64MB
1Gb = 128MB
So, if you take 8MB as the average rom size, you can fit around 2 roms on 128Mb, 4 on 256Mb etc. You can get other software that converts say an image into a tiny .gba file, so you can view it on the GBA/DS. Movies, Ebooks and Emulation of very retro systems is also featured.
HIGHLY RECCOMENDED FOR ANY GBA OWNER