It's not easy to spam someone on Nostr. The apps that users use have multiple options that make it into a non problem. There is a lot of spam and offensive content, but you just don't get to see it unless you look at "global" feed and that's now quite hidden in most apps. Essentially your app restricts to seeing content from people you follow and then you limit visibility on random replies to posts.

Now nostr is actually much bigger than "twitter-like" app, including powering app stores, chat apps, collaboration, podcasts, music player, etc.