Loved seeing this history firsthand. The Grist Mill was interesting, but not sure why it is part of this, or any, package (other than that it's too obscure to otherwise draw attention and this helps attract visitors and money to maintain it). Plimoth Patuxet was excellent, but would have enjoyed having a knowledgeable tour guide to learn from and interact with.
On the negative side, the directional signage was poor. If you're not on a tour bus or driving, once you arrive on the train at Kingston, you're pretty much on your own with Uber or walking, since there are no busses or shuttles. Plimouth should do a much better job, especially given the tourist trade. Also, be forewarned that Plimoth Patuxet is ~ 3 miles west of the other sites... a long walk or Uber. There should be a shuttle, even if just a few times a day.