A dog can hit the end of a long line much harder than he can a leash.Again, if you are afraid of this happening.... do not put a long line on your dog. Or leash. Or collar.....
Because if you will not step on a leash or hang onto a leash to stop a dog from lunging after something.... what is the point of having it on the dog?
I’ve stepped on a leash early on in his training if he got too excited wanting to meet & greet to prevent him from doing it. I’ve never stepped on a long line except that one time I did.
With a long line, I’ve used it to encourage him to come early on. I was told to drop it before a dog bangs into the end of one.