First of all make sure this is not a scam.
They only accept Money Wire and Bitcoins. The first will be hard to force them to refund, the later will be almost impossible.
Second you can calculate possible earnings here:
http://thegenesisblock.com/mining/a/6a7daabfcdBut the difficulty can jump anytime so there is no guarantee for a ROI.
My advice: stay away from pre-orders.
And only buy miners that are in stock and that it will be delivered within 3-4 days to your doorstep.