Byddai’n well 'da fi vs just well 'da fi

Going through the South course 2 and just started course 3. For the English: ‘I would rather not…’ sometimes it is ‘Byddai’n well 'da fi beidio’ but sometimes it just says ‘well 'da fi beidio’.

Are the two interchangeable? Or am I missing something on when to use bydda?


Missing out the byddai’n is just an informal spoken shortcut, so they are kind of interchangeable (depending on the formality of the context).
It’s like saying in English “better not” instead of “I’d better not” or even “I had better not” - the context infers what’s missing.