A few weeks ago I picked up the FCS-MM straight shaft lawn edger to use with my KM130R Kombi system. Brian has his review of the KM130R and various attachments here:
I used the edger to put in 1000' (technically 1020') of 12 gauge wire for the invisible fence for my dog. The FCS-MM takes about 3 seconds to attach to the Kombi powerhead (as all of the attachments do), and is up to the usual high quality I expect from Stihl equipment. The edging blade is more or less a rectangle of .2" steel and while it doesn't really have any type of sharpened edge on it, it will cut through small roots (under 1/2") without any trouble. If it DID have an edge on it, within 5 seconds of me running it through rocks the edge would have been gone anyway.
If you need to cut an edge along a lawn somewhere, I think this would be a useful tool to do it. We have a big hosta plant at the corner of our driveway, and the edger sliced right through a giant chunk of the roots that had grown out over the driveway the past few years.
As for cutting a 1000' slice in the ground to shove an invisible fence wire into, I am glad that project is over! For one thing, in normal use you can run the edger going forward. What I mean is, the edger sticks out in front of you, and you walk forward. If you are edging, it works fine. If you are trenching, it sucks. The rotation of the edger causes it to push the dirt into the trench behind it as you go forward, and it ends up basically filling the narrow trench back in. So I had to walk backwards for 1000'. This wouldn't have been so bad except some of my trench was through weeds and a patch of raspberries, so I kept having to look backwards so I didn't trip over stuff.
Also, now I understand about the tall guys wanting a string trimmer with a longer shaft so they don't have to hunch over. For normal edging where you just walk forward along the area you want to edge and let the edger do the work, again, it is fine. For pulling the edger backwards and keeping some downward force on it so it keeps digging the trench, I could have used something a foot or so longer. At one point I was thinking how could I strap 10 pounds of weight onto the thing, but I figure that would have certainly broken something. As it was I completely removed the adjustable rear guide wheel to get the blade to dig down as far as possible.
The other thing is that if you were edging a lawn, you would hopefully just be running through grass. Well there were several sections of my fence line that crossed over spots were I drive the tractor a lot, so it is packed down a little and there isn't much grass there, but there is plenty of shale. The edger doesn't edge rocks very well. Another thing to keep in mind is if someone is edging a lawn, they probably aren't going to do 1000' in 24 hours. That is a LOT of edging. I'm guessing in normal use a person might edge 1000' in two years.
So, I have it, I used it. Will I ever use it again? I'm not sure. My lawn is far from manicured and tufts of grass growing over the edges of the driveway or sidewalk don't bother me. 56FordGuy joked in Brian's thread that I should just use the subsoiler for putting the wire in. I would seriously consider it if I ever had to do this again.
Oh, yes, the invisible fence works well. I am still training our pup, but he is getting the idea. I wish I had video of the first time I took him for a walk and brought him near the fence. I never saw a dog move like that before.