Well, we've used retractable leashes for a couple of decades now. No injuries, other than a bit of rope burn behind a knee one summer. We use the ribbon type, rather than the string ones.
We live in the bush in Yukon; people often ask why we leash our dogs here when they could be free. Porcupines. Wolves. Coyotes. Mama moose. And more. So the 25' retractable leash lets them explore and play, but they can't run off & disappear for hours, or become snack food for a wolf or coyote.
Yup, they are under our control. The lock mechanism gets used when needed. When we're in a campground, it gets locked at about 10' but might be shortened to a couple of feet if there are loose dogs around.
When they do chase a squirrel or varmint into the trees, they know how to weave their way back out following their leash, so no tangles.