Plug in 333 Mh/s for $250 into any of the calculators that take into account an exponential rise in difficulty and you will find that these never break even. If the difficulty is rising exponentially, which there are strong indications that it is, these items will make less and less at a rate that means they never pay for themselves at any power use or electricity cost.
I plan on running some and selling some on Ebay. Profits from Ebay means I won't need to cover the cost of the ones that I do run.
That's one way to do it.
Another is to replace existing gpus with these (aka sell gpus that already earned themselves out) use the profit from that to buy usb devices. Net effect - keep your hashrate - lose most of the electric cost. That's what I've done. Sure they're overpriced if I were using them to grow my farm but replacing gpus means these earn themselves out in a ~3 months based on power costs.