Which Rebills Better? Long Trials Or Short Ones?

Just wondering if anyone has tested things to figure out which rebills better - a “long trial” or a short one? For example if a sponsor does “half off the first month” is a month such a long time that people forget to cancel? I can see if you had a 2 or 3 day trial it’s fresh in people’s minds and they might be more likely to remember to cancel. Anyone with hard data who can say which works better?

And yes, I know this goes to “what is a trial?” Half off the first month may not really be a trial - but for the sake of this discussion, let’s just say it is…