i would add it , it helps keep algae out and adds cetane to it (like power service) to help aid starting, as well as give power. It makes up for the ultra low sulfer fuels and adds lubricity to the fuel which sulfer use to do, which helps with the injection pumps. Many also will add a two stroke oil instead of a power service or mystery oil, at around the 300:1 ratio to make up for the new fuel. The additives help keep injectors clean and for a small 20-35 hp tractor a $5 bottle will treat like 50 gallons which will last a long time in a small tractor for someone who only puts 50-100 hours a year on a tractor.
I use it in my 30 yr old yanmar to help keep injectors clean and for the lubricity of it as well as the added cetane (says it increases the power, more energy so more power out of a gallon of fuel). Beleive in it if you want to, even if its snake oil it cant hurt from anything you read and the $5-6 i spent there hardly getting rich off the bottle i have had for 6 months and im hardly getting poor for buying it.
-nate