Yep, the toughest thing with an ATV sprayer is driving at a constant speed. That is what makes a tractor mounted boom sprayer more accurate. Keep in mind , most herbicide for food plots should be delivered on a per-acre basis. Fill your tank with water and go spray a field trying to drive at as constant of a speed as possible. When the sprayer is empty see how much ground you covered in acres. Lets say given your pressure setting and driving speed you cover 1/2 acre with a tank. Then if the chemical you are spraying call for 2 quarts per acre, fill you tank with water and add 1 quart of chemical and go spray a tank. This should deliver the right amount of chemical. A boomless sprayer still won't have the accuracy even when mounted on a tractor simply because it does not have as even coverage laterally from the sprayer. A boom sprayer mounted on a tractor can deliver a pretty precise amount of chemical.
Best of luck,
Jack