I tried to advertise a product to a very niche group on reddit. I just wanted to select 4 specific sub-reddits and advertise to anyone that was a member or viewed that reddit.
For some reason, reddit wouldn't let me advertise to 3 of the 4, and the 1 that they did let me advertise was very low volume (less than 100 members). I couldn't even get reddit to show a single ad, let alone have anyone click on it.
Facebook brought in way more traffic, and some of it did convert, but I feel like my advertising costs were too high there, since you can only specify more general interests. It seems like reddit, had their advertising platform actually worked, would have been the perfect place for me.