I never use them.
I don't advise my clients to buy them either, it just teaches your dog to pull. Especially our little guys more so than larger breeds. You want more leash? You just pull to get it! is the message they typically get.
Then when your pup is on a 6' instead of the retractable people wonder why their little one is choking himself at the end of the lead (this could still happen even if he/she had never been on a retractable though.)
Either case, in regards to safety? If never personally heard of an injury related to the use of these leashes. Walk on I say, use 'em if it appeals to you!
