I'll add to this: of every website I use which recommends me things based on other things, Reddit does it the absolute worst. It's so bad that they have literally never recommended me a subreddit which was actually relevant to my interests.
My favourite instance was when they assumed I liked "programming", based on having (accidentally, once) visited the /r/f5networks subreddit, so they suggested the Europa Universalis 4 modding subreddit.
Lately, they've given up and are just recommending me "gaming" related subreddits, by which I mean literally any random subreddit that it thinks is related to "gaming", including subreddits for people who main a specific fighter in Super Smash Brothers or subreddits for random indie iOS TCG games.
The only "recommendations" that seem remotely reasonable are basically trending posts, and that's just because them trending indicates a broad appeal for that specific post.
Meanwhile, their mobile app is wildly unreliable; if I'm having any sort of network issues while I start it, it will fail to load any of my feeds, and then just refuse to try to load them until I kill the app again. Refreshing my feed will typically result in a new feed with new posts, about half of which have no text in them and just a giant blank space where the title and description should be.
Reddit is a colossal nightmare, engineering-wise, and I wouldn't listen to a word they said about implementing technology.