I see some string labeled "Profession" or "Commercial". Are there any real world advantages to them?
I doubt it. They're all made of nylon monofilament. The only difference I've ever found between trimmer lines is the thickness.
Some have a ribbed profile (supposed to be cutting edge), but I agree with the above that they are all pretty much alike. I've used round as well as profiled with no real difference. This includes .080 of a throw-away Homelite curved shaft, .095 on an Echo SRM2100 semi-pro, and .105 on an Olympyk professional.