Spring WebFlux? pros, cons?

Can deal with a much higher volume of traffic before falling over or requiring horizontal scaling, especially if you're dealing with a scenario where you have to hold lots of connections open for a long period of time (websockets being the classic example.)

On the minus side - it's a completely different way of coding, it's very easy to screw up, it's very easy to make your code completely unreadable, there's very few experts to help you when you need it (especially on Stackoverflow and the like) and you'll also need to learn StepVerifier et al for unit testing with any degree of sanity.