J has revolutionized the way I think. I can confirm it: ever since I learned to program with it, I’ve been able to solve so many problems that previously felt far beyond my (limited) intellectual reach. For me, J (and by extension, the APL family more broadly) has contributed as much to my thinking as the methodologies I learned during my university studies in philosophy. Suffice it to say, it has profoundly and positively shaken me.
Answering for myself, I started looking into APL, but at the time, learning the keymaps for the symbols seemed difficult, so I started learning array lang techniques with J, and ended up liking it.
Some of the knowledge you acquire from one array lang can translate to the others, but the semantics are not 1:1 (ie. J is not just ASCII APL).
As it currently stands, I dabble in almost all the array langs, but of the ones I use, I think best in J. It's got a lot of convenience in it's large set of primitives, and there's no "indirection" between the character you want, and the one you type. Still, it's not without it's shortcomings.
I think I would probably still recommend BQN to most people looking to get into array programming, as it removes some warts in APL/J.
You lose some convenience functions (base conversion, fixed-point, etc) but you get a language which is more uniform and intuitive. And FWIW, I had the keymaps learned within the first day I started to play with it.
It's still a learning curve regardless of which lang you learn, but it will change how you think.
