I've seen early proposals of this and never been a big fan of the syntax, I'm di...

I've seen early proposals of this and never been a big fan of the syntax, I'm disappointed it made it in to C++23. Monads can be useful if they enable composition across different concepts, but this is syntactic sugar that IMO can be expressed in a nicer way with an immediately evaluated lambda and early returns.

Compare

    const auto ageNext = fetchFromCache(userId)
        .or_else([&]() { return fetchFromServer(userId); })
        .and_then(extractAge)
        .transform([](int age) { return age + 1; });

with

    const auto ageNext = [&]() -> std::optional<int> {
      auto user = fetchFromCache(userId);
      if (!user) { user = fetchFromServer(userId); };
      if (!user) return std::nullopt;
      return extractAge(user) + 1;
    }();

If you allow GCC/Clang extensions, the first two lines in the lambda can be even turned into

      auto user = fetchFromCache(userId) ?: fetchFromServer(userId);