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what is the ROI period?
Use http://www.bitcoinx.com/profit/ to calculate it as it assumes a profit decline into the equation.
I got 63 days based on 6BTC @ $170ea 0.15c/kWh power but prices move every day who knows tomorrow or how long it takes to deliver?
I checked too, that's good!
Would you recommend?
That calculator assumes decrease of profitability over A YEAR and the default is set to 60%. Difficulty has been increasing 40% every 10 days or so.
...so it's not accurate?
Of course we very likely won't see 40% increases each period over the next 12 months, however the take away should be that yes profitability will almost certainly drop far more than 60% in a year.
Please correct me if my 13m figure is off, it's been awhile since I've done much math.
By my calculations At $170/btc and $0.15 / kWh its going to cost more to mine than what you return after around 70 days at 40% increases, so you dont even have to look at it a full year.
Even at the rate as of this posting which is $195 / btc that would only buy you a few more days at 40% increases.
Its almost like the inital calcs were made (intentionally incorrectly) by hardware makers to help push sales.