Lbrown,
There are two manufacturers, Peco & 4m. They are for all intent and purpose an electric weed eater that mounts to the side of your mower deck. The Peco unit is a little primative and costs ~$400. The 4m unit is more refined, but the refinement comes with a cost, ~$850. The question with both units is what effect it will have on the mowers electric system. I have heard stories both positive and negative, no pun intended. 4m has came out with a hydraulic unit that is driven off of a stack pulley on your deck. They claim you can ride as fast as you want , no matter how tall the grass and not stop the trimmer. This alleviates the electric issue but obviously at a cost,~$1800.
My curiousity is two fold. I not only have 3 miles of vinyl 3 rail fence to maintain but Iam considering becoming a dealer for the 4m units. It is a large investment to become a dealer. I have done extensive research with the design and construction. Know I am trying to find someone, not refered by the manufacturer, who has hands on research . There is a vast cross section of people, from all over, on this forum.I would think that someone would have some input. If you have any questions please feel free to ask, I can probably save you a lot of time.
Ron