Are retractable leashes safe?

This is the category's biggest disagreement. High-trust threads in r/dogs and r/Dogtraining warn that retractables hold tension on a thin line, make loose-leash training harder, reduce control, and can fail mechanically. Many verified-purchase owners and some experienced large-dog owners still like them for sniff walks in open areas. The consensus is that they're a situational tool, not an everyday training leash.