Instead of building USB Miners why won't you build something like this.
Put the most chips you can on one board, since its lower power it probably won't start a fire like the Prisma. I can see it running at 5-6Th/s and using only 1000Watts.
Here is why. If you have a set of 3 or 6 usb sticks mining balanced on 3 or 4 pools you earn some btc with the standard pools and have a chance at a solo pool. If they can dial down to very low watt/gh it is possible to do a positive roi in a years time. and of course it gives you a shot at hitting the solo pool block. All this for very little out of pocket cash.
why would someone buy 6 USB stickminers that do <10GH/ea and cost likely >$10? A 100GH board could probably be done for <$60, and make way less clutter of the USB ports
small-scale mining is kinda pointless - economy of scale means if you spend $200 instead of $20, youll actually get >20x the hashrate and likely a better power efficiency. playing the 'solo lottery' with a USB miner is silly - its like going out and buying a dozen of those $1 scratch cards, instead of a 100-pack for $50 or a 500-pack for $200