I agree with Lis. It's a really good idea. But 6% sounds too good to be true.
The optimist would say that 6% is the real deal, but: nobody with poor credit has enough money for that 6% to be useful. Assuming the average person with a secured CC carries a positive balance of $300, that's $18 a year, versus say $60 in fees ($5x12).
The pessimist in me would assume some fine print: interest starts getting charged on the date of purchase, not only on unpaid monthly balances; and that the rate is high; and that the 6% is only on positive balance greater than current outstanding balance (ie, if you have $300 but $175 in purchases at the end of the billing cycle, you only get it on $125 for that cycle); and that there are other fines often found on financial vehicles of any sort intended for people with bad credit. The further pessimist would also assume that there is a per-transaction fee, including deposits (even direct deposit) and balance inquiries, and also that there is a maximum daily purchase/withdrawal. Because all of those things can be found on the exploit-the-poor cards that walmart loves and occasionally pays its employees with. (Scrip, anyone?)
At best, though, 6% on $5k is $300, and if fees are $60, that still leaves 4.8%. Pretty good for nice, liquid cash. Less good for less liquid cash (if they have maximum daily withdrawal/purchase.)