both will work and both do the same things.
the difference:
- the safc2 has a knock sensor indicator- but it really means nothing since nobody knows what the readings actually mean and they vary from car to car
- the neo has more tuning points and looks prettier (kinda- it has colors)
I upgraded to the neo from the safc2 when I got a killer deal for one, but after having both- it doesn't make a difference, and if anything, I prefer the safc2 to a certain extent, as I think that the neo's graphics are kinda ugly