Fish was weird at first, with it's insistence on `or` instead of `||`, and `and` instead of `&&`. Since they relented on this, there's not much non-POSIX weirdness for me. From time to time I'll try to `export` something, but fish just reminds you what to do instead. 3rd party integration is excellent now, too.

When I write scripts I'll just target /bin/sh, or /bin/bash if necessary. Never saw a reason to write zsh or fish scripts.

100% this! I tried fish, loved it, then didn't use it for about a year becayse I'd convinced myself posix compliance was important. The truth is day to day I use 5 or less shell language primitives, mostly I run other programs from the shell, and pipe them into each other, so the shell language compliance doesn't matter.

I don't understand this reticence about POSIX compliance. When would you need your shell to be POSIX compliant? I've been using fish for ten years and I've never had an issue, even with scripting. If I need to run a script, it always has bash in the shebang line, so it runs normally.

Am I missing something useful?

If you work with a lot of longer commands, you can press Alt+e to edit the current prompt in $EDITOR, so you can use your favorite editor to do whatever you'd like to the command.

Oh-my-zsh adds most of that while still being POSIX compliant

This whole time I didn't know you're supposed to use alt+s. I just got mad sudo !! didn't work. Thanks!