One of the great things about it was, it came with an assembler vocabulary to code your inner loops or other lowest-level stuff in. I gather BBC Basic had something like that, but I never saw and and I did get to use Forth in this way back in the day. Most of those systems made it harder to flexibly mix the higher and lower-level coding.

This is much like C. The easiest way to use assembly in C or Forth is to know your 'ABI' and write separate assembly code functions where needed. In Forth at least you can write a CODE word.