I think that Arrow is a really nice library, but if the team is just starting with Kotlin I would wait to use Arrow. Learn two things at the same time might be tough.

But once you pass this problem you should give Arrow a try. Arrow is based on Monads, just like RxJava, so it is not that much different. And you don't have to use Higher Kinded Types at all if you prefer not to. It is not much different than RxJava, you just have more abstractions and less operators, so you don't end up with a Observable trying to solve every problem of the world.

The main problem in RxJava me is that most developers tend to overuse it modelling everything as an Observable/Single/Maybe… You get an Observable acting as a List, as an Optional, Either… And then you deal with it by having an unbelievable number of operators. That's just wrong, but we don't see it because RxJava is so loved nowadays that we ignore the downsides. Don't get me wrong, Rx is great, but you simply can't have a Framework that don't have any flaws.

For me, Arrow can be an option to use a Monadic Framework do deal with problems, but to use it in more easy way. If you don't need to defer the computation, just don't and don't use an Observable. If it is not asynchronous, why to you need an Observable in the first place?

And one point that I love is: You should not worry just about the framework. By learning Category Theory (you're gonna learn some of it with Arrow) you are studying something that will last and will serve for many languages. Frameworks come and go, but the basics stays.

Hope it helps!