You need to determine how you need your sprayer to spray before choosing a product to buy. It makes a big difference if you are looking to hit the roof line of your home, garage, shed or barn vs spraying weeds in the yard.
You need to take into consideration the length of the wand as well as the type of spray the nozzle on the pump provides. The wider the spray, then less distance it will spray.
Most backpack sprayer go the distance of 20-25 feet.