Sorry Floridabear, your math is off. At $0.15 kw/h power cost, a Single is still profitable to a worthwhile degree even at 900 million difficulty. It's going to be a bit of time before we see 900 million difficulty, from 19 million now.
It´s understandable you don't want your devices called unprofitable. But - no offense - your post didn´t contain any math at all.
You´re using US-Dollar (power cost) as the base of your argument. You could do that. But what exchange rate Bitcoin - Dollar did you assume to come to your conclusion? Todays 100? Last weeks 120? Last months 150? Or the 13 half a year ago? Your reasoning makes no sense without that.
Or your basing your argument on Bitcoin. Thats of course only valid for those who bought your device with Bitcoins that haven´t been exchanged for FIAT. And even then, at least power costs have to be paid in Dollars - so you have to calculate break-even based on BFL price and power in FIAT. You see? Same same.
That said - and with all the love in der world
- maybe you should not argue break even or profitability of BFL devices seeing the difficulty going up immensely since months without a chance for your customers to participate in time.