Hi thanks for the input. Anapanasati is for developing the 4 mindfulness (mindfulness of body/feeling/mind/Dhamma) ["... mindfulness of in-&-out breathing is developed & pursued so as to bring the four frames of reference to their culmination"]. I tend to think the 4 tetrads can all be used for Vipassana to penetrate the anicca nature of body/feeling/mind/Dhamma, or bodily & mental formations. The penetration of the four (not only one) is needed for gaining insight on the anicca/dukkha/anatta nature of the five aggregates (body, feeling, and mind which includes perception, volitional formation and consciousness aggregates).
Yesterday at another forum I read a question concerning being mindful of body (or feeling or mind or Dhamma) alone can fulfill the mindfulness enlightenment factor and subsequently the other 6 enlightenment factors, which can bring clear knowing & release to their culmination, then why we need to practice all the 4 mindfulness ["This is how the four frames of reference are developed & pursued so as to bring the seven factors for awakening to their culmination" - MN 118]. The phrasing (or translation?) of MN 118 about this part is indeed a bit confusing. But I believe we definitely need to develop all the 4 mindfulness instead of only one, as mentioned above.
Metta to all,