</font><font color="blue" class="small">( Most any 3 point attachment you already have can serve as a counterweight. Also, are your rear tires filled with water?)</font>
Like you, I usually have enough ballast on the back with some implement, but I had noticed a lot of questions from people about these and thought it would be a nice easy alternative to making something.
Since these don't take up a lot of space, they would be easier to use than say a big can filled with concrete or something like I've seen some posts of.
John