I was about to order the batch 8 but now I am having second thoughts about ROI.
Even with free electricity, the analysis here https://tradeblock.com/bitcoin/mining/a/JzZtkWrbEJb3LeJj28EoCk
shows that I would ROI on August 2016, assuming starting mining on January 2016 and ~5 billion difficulty increase each month (best case scenario). (purchase cost ~$2000, including PSU and customs fees)
Keep in mind that bitcoin halving will be about July 2016.
So why would someone buy a S7?