A lot of Reddits have "Recommended" or "Related" boxes at the side. Why don't you implement these as first, and then use the algorithm(s)?
I think when I created this tool there was no recommendations on reddit.
When it was introduced later on reddit I was contemplating about using reddit's own recommendations, but at that time it was missing a few smaller subreddits, so I just put it of onto the shelf of projects to try.