I tried out J a few years ago, and after that, tried out APL, on which J is based. I prefer the APL syntax to J's because it seems to be more readable, perhaps because the brackets are always balanced. APL's semantics are simpler, not having the hard-to-grok ranks or the hook & forks.

Entering the non-ASCII characters isn't too difficult. E.g. in NARS2000-32 for Windows, we can use the mouse at first to click the buttons, but it doesn't take long to remember the keyboard shortcuts for the most important non-ASCII characters.