In a Ponzi Scheme, the founders persuade investors that they’ll profit. Franko does not make such a guarantee. There is no central entity, just individuals building an economy.
A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Franko has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.
The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.