BTC rise in value is irrelevant when considering profit. If you purchase the unit WITH BTC, had you simply just saved the BTC, at the end of 3 years you would still have the same amount of BTC.
So if .58 BTC cost will return .58 BTC return over a term of 3 years, had you simply held and not purchased, you would still have .58 BTC.
And in 3 years, the Miner, and PSU, will be worth nothing.
Purchasing a S3+ at .58 BTC is 100% - Hands Down - Burning your Money. You are essentially buying a device that costs .58 BTC that will, factoring all the near impossibilities I listed, return .58 back.
It's a lose lose.
Strato
And that is why I said to do the calculation with different time frame. S3 will still have value in 1 year, just like S1 still has value today. If you sell the equipment when it still has value you can come out ahead. You would likely be able to re-use the PSU if you upgraded to newer equipment so no loss there.So if .58 BTC cost will return .58 BTC return over a term of 3 years, had you simply held and not purchased, you would still have .58 BTC.
And in 3 years, the Miner, and PSU, will be worth nothing.
Purchasing a S3+ at .58 BTC is 100% - Hands Down - Burning your Money. You are essentially buying a device that costs .58 BTC that will, factoring all the near impossibilities I listed, return .58 back.
It's a lose lose.
Strato
I respectfully disagree. The S3+ will have no value in 1 year. Even with just a 10% difficulty increase per step; in 365 days the S3+ would return an average yield of 0.00066 BTC per day on 9/20/15 - IF your power cost was 0. If you paid anything over $0.02 kW/hr you would be mining at a loss.
Who would buy it?
I don't see any value there.
Strato