Can this card cause any type of damage to your system?
Maybe if it were damaged and causing a short across the pins, but not really otherwise.
Is this still the only one on the market?
Besides the three different Neo Power cards,
Tototek also makes one, though I can't really recommend it. It only has 32mb of memory and is rather primitive in comparison, both in looks and design (it uses a parallel port instead of USB). On the plus side, it is cheaper and has a cheat function, but winners never cheat and cheaters never win.
Were can you buy a flash card?
Get 'em
here.
also is it good for one game or muti-games?
They'll hold up to 63 games, though realistically far fewer due to file sizes.