I have a feature request though, along with path filter for review-stacks, could we use github labels as filters as well. I'll probably put this up.
The idea would be: when enabling 'Use this stack as a template for pull request stacks' an additional field could be set to filter pull-requests with a specified label like 'review-stack' or something. Only those PRs with the 'review-stack' label will be run as a review stack.