Review my fuelly if you have the time.
I ran these on and off for a year. I track my fuel religiously.
Gaspods never delivered any statistically significant reduction in fuel usage over a year of fueling on my mostly highway commute of 200km each day.
I installed them and removed them over a years worth of tanks, so as to remove seasonality and any prevailing wind biases. There was never any meaningful difference in fuel economy, on or off with gaspods.
Every time I hear a glowing review, the person shouting praises is never able to back any claim with any kind of meaningful data, and then they eventually just disappear (Suzanne, creator of the thread, where are you?). Examples provided have always been small datasets 5 tanks, ten tanks, which from a statistics standpoint is unfortunately meaningless.
Don't waste your money.