I dont see how keeping it in btc would make it safer, its still 120 days.. Usd is always usd and this service is about making profits without having to do much yourself. If you want to bet on btc increasing or decreasing you should do something else...
If volatility is what attracts people, There's a place to do leveraged bets on BTC's movements called BTC.SX. It is amazingly risky... just so you know. I lost a good amount of coin there during the MTGOX shenanigans. and yes, big players were using it to potentiate their gains with their ability to move the market overall, they would do the usual Stop-gap sweeps to shake weak hands and catch the profit... i have never gone back to the place and would rather do a tour of fukushima... But all this BTC Vs. USD talk reminded me that for high rollers there's plenty of places to get the adrenaline pumping.