I don't see this as that good of a deal unless you plan on mining with it for three months and then reselling it.

Without using a cost to purchase, just the hashing and power usage, the miner runs out of capability against the difficulty and cost to power in three/four months.  Here is what I used to calculate, https://tradeblock.com/mining/a/c6c8f5957b

The default difficulty rise is at 47% per month, which is about average for just about three difficulty changes at 14-17% each.

Is there something in the calculations that I used that are wrong? 

I want the S3 to be good, I have 27 S1's mining right now and would like to replace them as they will start to cost more to run than they make before the end of August.