Ask HN: Paywall systems comparison?

I'm looking for a comparison or some experiences using the different turn-key paywall systems (Journalism Online's Press+, Clickshare, and Google Onepass for those who have managed to sign up.) After extensive Googling, I came up with nothing terribly useful. For anyone who has used these systems: could you give your experiences? What were your difficulties with integration or setup? Any gotchas to look out for? For anyone who has used more than one, could you comment on how they compare? TIA.