Spitting flames is more common with turbo cars, rotaries, and n/a engines pushing the limits (cam overlap and timing).
I think though the big problem with these power chips is they send a fake signal.
When the incoming air is cold you can safely add extra fuel to the mix to gain power, when its hotter mix the ecu will pull fuel out.
What happens with these chips (resistors really), is they tell the ecu 'yeah it's 30 degrees, go for it' but in actual fact it is 35 degrees (or whatever).
The damaging fact is that you are giving your car incorrect information to deal with, so 'bad info in equals bad info out'.