The developers we work with haven’t p usher back at all. We use Zeplin and they love the layout/spacing feature more than anything else. They said they don’t use the CSS as much more than a tough guide. They’re typically writing variable sheets in Sass or LESS, so they said Copy CSS isn’t terribly useful.
That’s just been my experience and how I work with it. There are certainly some trade offs when you use this method.