If you follow the directions on the bottle, STA-Bil is a good product.
If you use the train of thought that my grandfather did, "If a little bit of a good thing works, then four or five times the amount must be great" you will find that the improper mix can leave a coating on the sparkplug ceramic that can short the plug causing bad or no spark. Of course that makes one think the ign system went bad over the winter and not the simple thing.
The first year I had to get his lawnmower running, took me a few hours (and beers ) to figure out what happened. Found out by accident when I pulled the starter cord without a good ground on the plug.
It isn't shorted when it has a good high resistance human body ground....
The second year, was about an hour and that was mostly the "he couldn't have done it again" train of reasoning that prevented me from looking at the gas.
The third year, about 5 minutes of changing a plug and draining the gas to a bigger container so I could mix in enough fresh gas to dilute the Sta-bil.
No fourth year because I started winter-izing the mower.