Pull Type models were originally designed as a solution for uneven terrain. In many applications that have uneven terrain, the user will want a unit that contours to the land. Each of the units have wheels to stabilize the unit for those uneven patches of ground.
When we say, "self-contained" we mean that the unit comes ready to go. While you will have to assemble the unit when you receive it, you do not need any additional pumps/tanks to get started. All you will need is the chemical of choice and an ATV or something to pull the unit!.