Really cool! What's the biggest differentiator between Sequin and a secured credit card? Me and my wife used the latter as the first step to help build our credit history...but admittedly the limit was small.
How exactly is your card different? Is there no obligation to make payments? If so, how many cards can I open?
The only novel thing here is you are deceiving the processing networks by claiming your debit card is a credit card. My credit union tried to do the same thing many years ago (as a way to build credit for students) and it eventually got caught by the processing networks and recategorized. Within a month or two it dropped off everyone's credit reports and they were back to square one.
We are an official Visa partner and deal directly with credit bureaus.