The Xtreme linker uses a device which you connects to the pc using a USB or serial port.
For the serial port, an additional power source is needed.
With it's default writing software (Xtreme Link) or LittleWriter (unofficial software for
the Flash Advance, Xtreme, EZ Flash and XG Flash) you can put ROMs on the card and update it (e.g.
deleting a ROM and replacing it).
The 128M Xtreme card has trouble handling games like Castlevania HOD and Megaman Zero.
I recommend using the 256M Pro card.
Flash 2 advance has a cable which connects to a serial port and directly to the GBA. No additional power source needed. With the Flash Advance writing software, every time you write, the whole card has to be rewritten. Handling save games is complicated. It is not compatible with a program like LittleWriter.
Conclusions:
I recommend the Xtreme USB linker with a 256M Pro card. The USB linker is
compatible with LittleWriter and most important, I haven't found a game yet which doesn't work
on the 256M card.
Some links
Flash 2 Advance homepage
LittleWriter
Flash cards compared
XG Flash homepage
