It's worth testing to see if generating key is an important step or not. I think Damus and Primal both have you save your key. Snort on the other hand doesn't mention the key (by design).  Just need to measure the funnel entrance to exit (got to the feed) for each app to see which is more effective. My guess is they are roughly the same. 

As far as retention goes, I don't think knowing about keys impacts it, but content does significantly. If you sign up to something and see things you are not interested in, what's the point of sticking around? This is the super important discovery step we need to solve. Right now you just see some bitcoiners and in some cases trending people being recommended, but people often dont follow anyone, they just skip. Some clients offer hashtag following, but again, some people just skip all of that. I think this is why Twitter forced people to pick some topics so they could show a decent starting feed.