I have had an eline over my FMF pipe since the start which would be 3 years. I have noticed that the thing is starting to wear down to. The worm clamps are digging into the carbon fiber, and I have noticed some minor cracking in the outside layer which is starting to worry me. And yes I take it off to clean it and the pipe, or the pipe would probly rust out from the build up of mud. Of course it has done a wonderful job of keepin my pipe dent free, but Im beginning to wonder if it was worth forking out over 100 bucks. I'm not even sure if the thing will make it through another year of abuse. Also the eline claims to give a bit more power by elevating the temperature inside the expansion champer and burning off the gasses quicker, barely noticeble though. I might think about the Fredette guard next go around, even though it is still expensive, definately not as much as the E-line. I say go with Freds, best deal for the buck. Oh and the aluminum guards aren't much, a friend of mine has one, and his guard and pipe is dented all up!
I had pipe armor on my pipe, and it kept it dent free, but it caused the pipe to get bent at the first turn in the head pipe from an impact with a tree because it was so stiff. I think the pipe would probably only have dented without the gaurd, instead of kinking shut. I haven't used it since.