also could anybody give me a link or tell me how difficulty is determined?
Difficulty is adjusted every 2016 blocks. The intention is that it will take the entire network 10 minutes (on average) to find a block, so finding 2016 should take 14 days. If solving the next 2016 blocks takes only 7 days, difficulty will (roughly) double.
Whether this is a scam or not, I wouldn't buy any mining device that won't be available for four and a half months. There's no way of telling how high the difficulty will climb by then.
At the current rate, it's raising 30% every 11 days. That's 12 difficulty adjustments until February 24 (if they deliver on time), giving a difficulty of 4.4 billions.
yes but 2 TH/s is 2 TH/s it would manage those changes until february or you think it couldnt?
The earnings per GH/s are inversely proportional to the difficulty. Right now, it's at 189 millions. A 2 TH/s miner at a difficulty of 4.4 billions should generate the same income as a 86 GH/s miner at the current difficulty.