I think it depends on your location and demand for the developers with expertise in that domain.

For instance, Stockolm, Sweden is vibrant city with lots of startups and the need for good developers are constantly increasing. Stackoverflow careers is only used by very few companies and as far as i know, there has been good responses for those ads. I think its acts more like a filter compared to other routes. IMHO, There is a considerable amount of noise in traditional routes.