That feels oddly low. It was released at 5ish PM PST on a Wednesday, and considering they have literally all of Instagram + Facebook's userbase to push it on, it seems pretty low. The "sign up" was also just a "log in with FB/Instagram" button where the form was already auto-filled. So it's not like people had to convert, it's pretty much about as pure a product-market-fit test you can get. Discoverability is also pr…
Give them some slack. Twitter wasn't fully polished two hours after initial release. You need to give them some time to fine tune their algos and come up with new features. My bet is they will soon develop an explore page similar to Twitter's, and will give users options to tailor their home feed.
I think yours is a very critical take for a company that pushed out an MVP two hours ago.