HexFury is one of the USB ASICs with the highest GH density. It has a 11GH/s and is quite expensive. You are expected to earn around 0.01BTC per month before factoring electrical cost and difficulty increment. Did I mention it is $70 per? You are required to get a good USB hub to power all of them. Buying Bitmain S3 and better would give you a better chance at ROI.