@NotJustACigar, I've had injuries from both: a few trips, a yanked shoulder and few friction burns to my hands from the longline, friction burns to my legs from someone else's retractable. But I've used my longlines for hours and hours, many times longer than I've been near retractables.
The difference is that a longline is wider so more easily seen, and will give you a wide but shallow friction burn but will never give you the sort of really deep wound that a thin retractable can dish out. Also, if you wind a few turns of the longline closely round your hand, friction burns are much less likely. A dog on a clipped retractable or at the end of the line could give your shoulder just as good a yank as a dog on a longline. You can also let a longline trail (and I've used mine in woods and cover, I just make sure that I know where the dog is), plus it is much less likely to break than the works inside a retractable.
One of the things that I really don't like about retractables is that they teach dogs to pull. Pull a bit, lead extends... This is absolutely what you don't want a dog to learn, so unless you are rigorous about the dog walking to heel when told to or on a different type of lead, I suspect you will end up with a puller.
As I said upthread, I can think of circumstances where a retractable is helpful, but on the whole I don't like them.