I just found out not long ago that Echo uses flex shafts in all their line trimmers, I was quite suprised! As noted before, flex shafts need to be removed, cleaned, lubed, and reinstalled on a periodic basis. As flex shafts age they tend to have more vibrations due to the metal fatigue and flexing(bending) in the shaft under load conditions. Solid shaft do not have the "flex vibration" problem until the shaft bushing wear out. Since most solid shafts are stainless steel, only the shaft housing has to be replaced unless the spline are worn out. Under heavy load conditions, such as brush cutting with a blade, flex will not last near as long due to the extra torsion stress place on the shafts. When cutting brush that has a large diameter that has a heart core the brush will cause shocks to the shaft. It not pretty to see a flex shaft that has been grenaded in the fashion.
If you are not doing brush cutting the flex shaft will probable hold up for a long time, if properly lubed on a regular basis. I recommend solid shafts units only when other people in my department ask me for my recommendation.
'

'As a note on line trimmers: Ask your local dealer for a demo on a Robin 4 cycle line trimmer. We tried one for a week and was very impressed. Same size fuel tank, ran 2 to 3 times longer on a tank of fuel. Massive power, used .105 line in it. Just slightly heavier than it 2 cycle counterpart, hardly noticable. Unit has a 4 ounce oil resevoir that need change every 40 hours of use. We thought the power outweighed the inconvience of the oil changes. Oh yeah, very quite, if you wear ear plugs you can hardly hear it.
