Personally I draw the line at leashes. But it depends what public means. In more adult spaces, especially somewhere like a club or a dance I see no problem at all. Collars are just sort of like chokers. They just look kinkier.
To be clear I don't think people shouldn't be allowed to use leashes anywhere or whatever, that's just sort of where the personal line is for me. As in if someone asked me "Hey, should I leash up my sub while shopping" I'd say "probably not". It's not like I'd ask someone to please remove one if I saw them.
She like flirts with him and says she was into him or something. It's weird as hell. A good movie though. Just a weird part. It's like the execs were like "we can't have a movie without a romantic subplot!"