There's like 50+ reasons NOT to.
1. NO device with wiring to it that small will be setting ALL voltage in a car even, the wires are comically small for that.
2. Any complicated electronic device in car like ECM or TCM or BCM already has a voltage stabilizer/limiter in it.
3. Better gas mileage? You gotta be kidding! I should also point out the injectors REQUIRE varying voltages to even make the car run right.
4. You DON'T want voltage stabilizing, the alt ramps up and down based on loads, stabilizing volts there means stabilizing amps too and a huge mistake. Not doing it means the battery cannot charge up more when worked harder. The volts if stabilized at that point can now miss whether the charging system has a fault or not. You WANT to see the ups and downs.
5. Wanting one makes you out to be a sucker, plain and simple. Need I say more?
6. It is simply a digital voltmeter, available all over the place at $5 a pop.
7. The plug there appears to be the super cheap Chinese type that breaks up in pieces like the 3rd time you use it.
8. If you WANT voltage stabilized then make up a little box with the voltage number simply printed on it, it will work as well as this device does. You don't even need any wires, you can claim yours is better because it's wifi to the car's charging system and computers, and also tied to the earth's magnetic field to stop global warming. GUARANTEED, that printed number will NOT be changing, that's as stabilized as anything could ever get.
9. Voltage sensing as a late development? (post #8
) Alternators have been voltage sensing for 70+ years now.
The perfect device for witless purveyors of a 'truth is not truth' world.