With a bad back, lugging around a weedeater is about the worst thing I can do. I have one of the walk behind push weedeaters, but that isn't much better.
Came up with this today. I can adjust the height by sliding it forward or backward in the bracket. The throttle is run with a string tied to the little board that I can push down with my foot.
It's not perfect when you get into uneven ground but, with a little maneuvering, you can get everything pretty straight. I wouldn't want to trim a finely manicured lawn with it, but it works great for everything around here.