USB miners? when did this stop being useful?
USB miners have no cooling, therefore you can't put efficient ASIC chips there. Also, after so much more efficient ASICs came out, the difficulty skyrocketed and they are unprofitable. These are only for collectors and people who want to mine as a hobby but do not want a big and expensive ASIC which emits a lot of heat.
Say what? Efficient means less wattage per GH/s produced. Efficient chips are exactly what you need to put into a SUB stick.
The reason they are no longer made is that the housing and interface for the USB miner is more than the cost of the chip itself. Compare that will industrial miners which have hundreds of chips and only 1 power and data interface - economically it's inefficient to make a USB miner.
