You can set your project / environments to be public, and then anyone with the link can view it. This is useful for the one-off reviewers you mention – you won'

You can set your project / environments to be public, and then anyone with the link can view it. This is useful for the one-off reviewers you mention – you won't be charged for these users (viewers). However, they won't be able to comment / perform writes. You have control of who you invite to your FeaturePeek team, whether it's a subset of your GitHub org or people outside of GitHub. You'll only be charged for the users you invite.