> This shouldn't even be proposed as a question to someone new to Haskell. They should learn how monad transformers work and just use them. 90% of developers playing around effect systems would be just fine with MTL or even just concrete transformers. All Haskell effect systems should be considered experimental at this point with unclear shelf lives.

This is highly debatable. I would say that the effect systems effectful and Bluefin are actually significantly simpler than MTL and transformers, particularly as soon as you need to do prompt resource cleanup.

Personally I'd say that if newbies should start with naked IO and then switch to effectful or Bluefin once they've realised the downside of IO being available everywhere.

> All Haskell effect systems should be considered experimental at this point with unclear shelf lives.

effectful and Bluefin are here to stay. I guarantee it. For non-IO-based effect systems (e.g. polysemy, freer-effects) I agree.

(Disclaimer: I'm the author of Bluefin)