i personally know people that have bought shares and cashed them out after the 120 days. and coupled with the fact that i havent had a single issue with withdrawing funds daily... the question is... how long do you have to wait before you consider it "legit"?
It's a ponzi today and it will still be a ponzi tomorrow, so never. Unless they drastically reduce the payouts they will fold this year or the next, though. Madoff only paid about 10%/year, which is part of the reason why his ponzi lasted for so long.
I actually think their results from arbitrage are reasonable. I was involved with the btc-arbs drama, and there has to be some money in arbitrage as the operator of that service is purportedly repaying depositors with arbitrage funds. To my understanding, he's no longer accepting deposits but is paying depositors back. I have received payments and can verify this.
I also think they are still trading with depositor money on weekends and holidays and keeping those profits. Not exactly ethical, but if that motivates them to keep this thing going, our incentives appear to be aligned.