It basically gives you the option of receiving an 18% cash refund or a 21% voucher, according to your payment amount.
Miners ordered after a certain date get a 25% refund or slighlty higher voucher, afaik. (as the hashrate was then advertised as 6Th)
Don't think the 2nd sentence is accurate.
Further to my post a couple of pages back and an email to Spondoolies I bought when it was 6-6.5TH and was told they understood but the 18%/21% was the best they would do.