We do the best we can,
and we can always do better.

The techniques are skills, they take practice. A lot of practice. They become part of how we relate to ourselves and to our loved ones, and to others.
Internalized, these skills transform our own sense of self, no small thing.
Initially, the skills are about having an effect on our BPD loved ones. Over time, they become part of our own overall emotional health.
We become the beneficiaries of this work, strangely enough.
There are a lot of variables, so this is not science.
As you know, it is extremely difficult to work toward emotional health when the person you love is tearing herself and you apart.
It is very difficult to (effectively) love someone who does not love themselves. I used to think that described my BPD loved one, and then I realized it applies to me as well.
When you focus on taking care of yourself (loving yourself) and working out what it means to be emotionally healthy, then you're in a much better place to apply skills that can be effective in BPD relationships. I think that's why we can read such different opinions about BPD relationships. It can come down to whether or not the person opining turned the arrow around to face themselves.
That's pretty tough to do when the person you love is acting way worse than you.