I like Flexi retractable leash products because they work for me. My dog wants constant and even pressure to 'keep tabs' on me (who's on the leash, and who is in control, here?) Flexi leashes have an ideal spring tension; the knock-off and rip-off models (at Walmart) have too much tension and far less functional locking mechanisms and abominable ergonomic design compared with Flexi leashes.
Detractions are that the user can get rope burns from the cord (It's happened to me a couple of times in four years, but my dog is not a puller or a runner (at least while on-leash), and the cord will wear through from friction and abrasion under the collar where the cord is knotted to the snap at your dog's neck. Both of those issues are probably less of a problem with the tape model of Flexi leashes, but the tape model I had was affected by the wind to an extent that neither I nor my dog liked.
Overall a good product. Overpriced, but worth the difference due to value and functionality.
This is our 4th 10' leash by Flexi over 8 years and two 30 lb dogs. I like this shorter leash over a 16 ' leash for better control in crowed situations and cactus.