I've never heard of a concatinative programming language before this. I can of course google, but since you obviously find these languages very interesting, I'll ask: what's a first, interesting thing I should know about them?
Concatenative programming is interesting in that the arguments, in and out, are implicit because they typically reside on some form of stack or as objects on a stack. (implementation details)
It might sound useless but one benefit is it simplifies factoring code greatly. If you see a common phrase in your code repeated many times, you can just cut it, paste it into a new definition, replace all the instances of the common phrase with the new definition and everything still works as before.
This is a profound distillation of the essence of Forth. You can stop repeating yourself without the need to work out all the parameters, variables, return values, etc.
My experience is that when it doesn't work, it might indicate that the code is fighting with how Forth is easiest to use.
I try to use Forth per Chuck Moore's philosophy and use many small definitions. This makes the code more like functional programming such that even data is handled by code snippets. When I get this right, factoring becomes trivial.
Experienced Forth users seldom have that particular argument count problem but all the other mistakes in programming are on the table. There is no free lunch.
The Forth coding process involves using interactive testing of your code as you write it. Every variable, constant, data-structure and sub-routine can be easily verified at the interpreter. And... given what you said it is advisable to do it. :)
ANS Forth supports local variables for those times when "stackrobatics" might make you crazy.
Although small, the Forth community has made good progress in this alternative way to code. Some of the newer concatenitive languages working with a clean slate have gone farther in improving the programmer interface. Forth remains at its core close to the metal.
Is a 1.2 million LOC large enough? https://ribccs.com/solutions/solution-candy Written in MPE VFX Forth, native code compiler for Windows.
*I have no connection to MPE UK but have used their cross-compilers in the past.
I would say that the most interesting thing you should know about them is that practically everything they do is manipulating a stack (actually, there are usually two stacks, I don't know if this is the case for Stabel).
What I find more interesting about them is their simplicity (comparable only to Lisp), which makes possible writing a basic interpreter in only a few lines of code. Being more concrete, an important property of concatenative languages is that they allow a point-free programming style, which gets a bit to get used to but really makes you think in a different way.
If you already feel curious, I would suggest the book "Starting FORTH" before looking into more modern (and practical) alternatives.