Oh good point patientandclear-- I think it would be triggering for me as well (thinking about all the things I could have/should have done).
I did because my daughter shows incipient signs of BPD. One of the gifts that keeps on giving from my BPD love relationship ... .I was so destabilized by what happened with my ex that I regularly dissociated (literally "lost time" at night whenever I would sit down and thoughts of the r/ship would pass through my mind) and was sort of emotionally absent for my kid at a time when she needed me not to be missing.
The skills are useful for me in working with her and when I have communicated with him, somewhat useful there; but also hugely triggering for me, as I spent a lot of the class seeing how I could have handled things differently with him and maybe we would not have come to a dead end.
My own therapist had to keep saying "these skills were developed for someone who is not coming into the dynamic seeing the other person's side, considering other points of view. They are somewhat extreme to nudge people with BPD toward the middle of the continuum. If you already have distress tolerance skills for instance and don't run away at the first or second blip or inadvertent misstep, you may end up thinking with these skills you should endure or try to endure much more harmful behavior than you should."
My teachers were actually also good on this point. They would say "distress tolerance is to prevent impulsive reactions while you gather yourself to engage in deeper problem solving, not as a mechanism of making circumstances that are not OK, OK." But ... .I could see the partners of BPD folks who were in the class getting fairly good results from using the skills with their spouses and it would constantly make me doubt whether I did the right thing at various points in drawing lines with my BPD ex that have resulted in us, at present, having no contact--rather than using these more nuanced skills. I'm not sure taking the class was healthy or helpful for me over all.