K100 fuel additive

Do you really need fuel additive?
I have lot of seasonal equipment and used 7 yo diesel just fine.
Gasoline is more tricky, but I had boat with 3/4" open vent and even after 2 years the gasoline would start the engine, although with excessive smoke.
My Honda lawnmower runs on gas from previous season just fine, but I always shut off the fuel and run carburetor dry at the end of season.
In some climates water condensation is the biggest issue, but I have never seen it in CA.
Seafoam is mostly kerosene.

I used to use Stabil but changed to Sea Foam some years back. My personal opinion (FWIW) is that SeaFoam work far better than StaBil. Available at your local WalMart.

They probably recommend it because the make a higher profit margin on it. Without some sort of testing, how would anyone know if its better. I have used Sta-bil for many years and I can tell you it works.