Open headphones sound a lot less canny at a lower price point. They do leak sound in and out, but whether that's an issue depends on how loud or quiet your surroundings are. If you're in a noisy environment, it'll ruin your enjoyment of the music. Most environments - including parks, lakeside walking paths, doctors' offices, etc., aren't really a problem. On a rumbly vehicle, like a bus, your bass will get canceled out. In extremely quiet environments, the sound you leak could be a problem. You could easily listen to open headphones in a library as long as you didn't have the sound up too high. The hardest sell is bed. My wife hates it when I wear my open cans to bed (so I don't). But I can listen to my music in the living room while she's watching TV and neither of us are the worse for the wear. It really depends on how invasive either sound is, but the fact that the driver is so close to your ear tends to make your music sound a lot bigger to you than to anybody around you.
The idea that open cans are useless or invasive in all but the most secluded environments is an exaggeration parroted by people who don't wear them.