USB mining is an obvious dead end. Mining is fungible and prone to economies of scale, you will only survive with a massive datacenter, the best ASICs on the market tightly packed on the cheapest boards powered with the cheap energy. Large discounts for purchases, effective workmanship etc. enable you to undercut the competition by pushing more GH/s for a given BTC price. You get more of the mining pie and maybe a thin profit margin.

Compare this with an USB stick where the form factor alone (with USB controller and connector, plastic case etc.) has increased the price 10x as compared with the bare mining chip. Nevermind that in order to run say 10 USB dongles drawing 2W each, you need to power a whole desktop computer with at least 50W.