I don't know anything about wii stuff, but I know that the Sinden lightgun kicks ass. It's certainly the one you want to get.
To make it work, you'll need to enable the experimental "absolute positioning" configuration for lightguns:
look in your config/fbneo.ini file:
// If non-zero, enable lightgun positional mode (Sinden or real lightgun HW).
bBurnGunPositionalMode 0
set that to 1, and it should work!
best regards,
- dink