I don't think that's likely to be an issue in this case because the ads are not presented in a standard ad format, instead they are part of the usual list of reddit items.
For a cool new consumer product or service that makes money directly, though, this could be great. When I tried it, the CPC was very low. Whether it's worth it depends on how good a fit the thing you want to advertise is with the audience of Reddit.
I can't imagine making a great return selling something directly on there unless you product was so cool that a regular post would have had nearly the same effect.