Yeah, I'm not super familiar with Raisin, but I'm not sure I see a significant benefit for the end user. Just go directly to a bank with a high yield savings account and open an account. Mine's with Bask Bank.
And I sure don't I like the idea of a "free" service that acts (seemingly unnecessarily) as a middleman for your various banking accounts... The old adage goes: "If the service is free, you[that is your data and personal information] are the product".