I bought one when I first started out 5 yrs. ago. They could be useful if all you are trimming is sidewalks. Along curbs where grass aprons may not be level you will get better results from a stick edger.
We have been edging all our properties monthly with a blade edger per our contracts since day one, so when we upgraded equipment after the first season, I did not upgrade the discs.
One thing that I liked about the disc was for "newer" employees on trimmers it did help them gage where the trimmer should be so as not to scalp while line trimming around the landscape.
I like my edge-it but agree a blade is better as it can be kept a little closer to the cement. Edge-it takes some getting used to , is great under cyclone fencing cause it keeps the line from hitting the metal and getting cut . Also is good for extra tall grass as it keeps it from wrapping around the head. I like have an edge-it, a trimmer and a blade edger.
Everybody I mean Everybody here in Hawaii uses there T-27 line trimmer for edging. I always have and it works just fine. I learned two ways to use it as an edger. Do as the owners manuel says or turn the beast on its back, stand parellel to the sidewalk facing the edge and let er ripppppp. With very little fatigue. Been doing this since 1985. I get super clean results on all southern grasses. Tif Bermuda, Emerald Zoysia, Centi, Augustine, Seashore Paspalum, Z-3 Zoysia. Etc., Etc. Oh and another benefit to my methodolgy, you get minimal ricochet effect as all the material flies away from your body particularly your face (sand hurts!). Also,I no mo room on my 86 Mazda Methuselah (189,000 miles on Amsoil) so me only needs one tool fo do da job. Hey does this method look unprofessional? If it does tell that to the President of the Hawaii landscapers guild, cause all his boys been going this route since the name Shindiawa/Green Machine.
However, I don't know how this would go over on the U.S. mainland. Just thought that you good people might want to know what we do here. I suppose that a designated edger whatever one you use gets the desired results.