Not only do you have to be careful of being outright scammed, but BFL ships not on order number but on payment date. Someone could very easily be selling a sub 3k order number that just got paid off this month.
However... even if you wait until they are actually shipping their product, you are likely to receive a quick ROI. Check out this handy calculator that takes into account increasing network difficulty.
http://bitcoininsight.com/2013/04/05/bitcoin-mining-profitability-calculator/