It’s not a replacement for react. It’s built on top of react and gives you all the best practices for SSR and development setup out of the box. It’s been highly optimized (including with help from the Chrome team), and is in use at some very large websites.

I can’t recommend it enough. Although if you’re doing anything with moderate complexity, it is still important to understand what’s going on under the hood. At least, you should know the difference between client side routing and server side routing, and any implications of when you might need to treat one differently than the other. I could see a total noob potentially getting hung up on that aspect of it. But the rest of the ease-of-use outweighs any complexity stemming from SSR, IMO.

It provides pages/routing, JS/CSS compiling/bundling, and even optional static site bundling. It's basically the missing pieces for a deployable react app.

Nextjs is an opinionated stack that specializes in SSR, routing, and bundling.

React/Redux are building blocks to your own "React Stack".

You can use other state libraries (like xState, MobX, etc) depending on your programming style (reactive, state machines, etc.)

It depends what you want to build. You choose how you stack it.