I have to agree with @jivetalker 's assessment that for $25/2gb is pretty sweet for 8 months. If you are a fairly low user and can switch to the $15 plan with 1.25gb of data!
I wouldn't be excited about this plan even if it were a permanent 2GB for $25. There are ways to get that much data with talk and text for $27 but get full LTE speeds elsewhere (on a full national cellular network). There's room for improvement in Public Mobile's plans.
The churn can be reduced if they make it immediately clear in Self-Serve what the conditions, duration, and limitations will be. As in, some kind of in-your-face message like "changing your plan now will disqualify you from getting the rest of your signup bonus data" or whatever.
And if they perhaps send SMS notifications every month which remind you that you got (or will get) that bonus data by sticking with the plan. Because too many people set up AutoPay and never bother to login Self-Serve again - unless there's a problem.
And if they perhaps send private messages to the linked Community account (if there is one) with the same information. Maybe overkill but automated messages cost nothing.
If PM basically takes away the customer's ability to "accidentally" (unknowingly) abandon the promo conditions, and if PM keeps the customer updated with promo details/status (instead of forcing the customer to remember and do math and stuff, lol) then the only ways left to "lose" the promo data are to intentionally ignore the warnings or to stick around long enough for it to expire. (And I'd bet that few of these customers would run off the moment their promo deal expires if PM just happens to send them a one-time "hope you stay" gift of 2GB just before the last renewal.)
Is this valid for existing customers?
This is still a good question.
The usual "new customers only" seems implied. But it's not explicitly stated. Probably just an oversight. But possibly an offer which is also available for existing customers.