It's the same if your Maybe<Foo>=Just<Foo>|Nothing, and in fact in that case I often prefer the nullable version, unless there's a dedicated, terse syntax for Maybe-checking built in to the language, the equivalent of null coalescing (Kotlin's ?: (Elvis operator), Typescript's ??), along with optional chaining calls (?.).

If you made a Maybe with a Nothing<String> that comes with a reason why nothing was returned, or any more complicated structure like that, then it's better[1] to use that instead of approximating it with exceptions, null, callbacks with an optional error argument, etc.

[1] In most cases. There's always exceptions, no pun intended.

My view is that `foo?` is a nice sugar for the common Option/Maybe/null case, but that a language is severely missing out if it doesn't also offer general sum types. I don't understand why more languages don't offer them, it seems like it'd be a fairly easy feature to add without breaking backwards compatibility.

Rich Hickey's talk "Maybe Not" has some interesting thoughts on this: https://youtu.be/YR5WdGrpoug