Definitely snake oil.
As far as I can tell from some very quick research this system makes adjustments to the ECU's airflow signal rather blindly. The system gets information from the throttle position sensor and the air flow meter and causes changes in the fueling of the vehicle by modifying the air flow signal received by the ECU (some times a piggyback will alter the TPS signal as well, but it is uncommon and never the sole means of modifying the ECU's fueling and timing). The change in
reported air flow causes changes in fueling and timing. The problem is that this is a completely blind change on the part of the Venom unit. It has no idea what air to fuel ratio its changes are causing nor does it know what changes are ideal for your specific vehicle. Sure there are trends in a given series of engine which can be used as a guideline for base changes, but every vehicle is quite different and those differences are amplified with age.
This "piggyback" falls between the "AMAZING SuperChip! +85HP instantly! Only ONE Wire!" and the original SAFC. I'm sure (I hope) some time was spent to find a basic map for changes but they're not going to be tailored for your vehicle. At least with the SAFC you have the control over the changes and you can tune specifically for your vehicle.
One reviewer may have it just right: "HPF was awesome in their customer service/shipping. However, the Venom ECU is a scam. All this system does is make your engine think it's at full throttle when it's not. Instead of spending $300, just push the gas pedal all the way to the floor. You get 0 top end performance gains from this product. Research items BEFORE you buy them."
Your money would be much better spent on a MAFT Gen II and a GM MAF.