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.
I believe this to be exactly the case. And if so, I am ok with that as long as I keep making my 20% per month... win/win.
I have looked at the mechanics of the arbitrage game myself and ALMOST created a similar platform. The real trick to making this all work is not in how they are making money (that's easy), it is in how they rebalance their cash accounts after the trades. With more cash volume it becomes easier to rebalance those cash accounts. With bitcoin it takes 10 minutes and boom you're done so volume isnt a big issues, but in order to rebalance the cash accounts you have to wait on wire transfers and the banks SUCK at this, even losing money on occasion. So with more volume in their cash accounts it makes it easier to rebalance faster for the next trade.
I have read it asked here before somewhere "why if they are so profitable would they want our money to trade on, why not just use their own and keep all the profits" or something similar... well that is why. very large volumes of cash are required to make the trading profitable for one reason... "cash account rebalancing".
So far I am VERY happy with how Bitcoin-Trader has done things.
If people want to scream "ponzi" ok... well time will tell... Be smart.
or just take a look at
https://www.btclegacy.com/ and let's begin talking about their "legitimacy".... I almost want to put money in them just to see WTH is the deal.